Device and method for scalable coding of video information

ABSTRACT

An apparatus configured to code video information includes a memory unit and a processor in communication with the memory unit. The memory unit is configured to store video information associated with a first video layer having a first picture. The processor is configured to process picture order count (POC) derivation information associated with the first picture, and determine, based on the POC derivation information associated with the first picture, a POC value of at least one other picture in the first video layer that precedes the first picture in decoding order. The processor may encode or decode the video information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional No. 61/890,868,filed Oct. 14, 2013.

TECHNICAL FIELD

This disclosure relates to the field of video coding and compression,particularly to scalable video coding (SVC), multiview video coding(MVC), or 3D video coding (3DV).

BACKGROUND

Digital video capabilities can be incorporated into a wide range ofdevices, including digital televisions, digital direct broadcastsystems, wireless broadcast systems, personal digital assistants (PDAs),laptop or desktop computers, digital cameras, digital recording devices,digital media players, video gaming devices, video game consoles,cellular or satellite radio telephones, video teleconferencing devices,and the like. Digital video devices implement video compressiontechniques, such as those described in the standards defined by MPEG-2,MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding(AVC), the High Efficiency Video Coding (HEVC) standard presently underdevelopment, and extensions of such standards. The video devices maytransmit, receive, encode, decode, and/or store digital videoinformation more efficiently by implementing such video codingtechniques.

Video compression techniques perform spatial (intra-picture) predictionand/or temporal (inter-picture) prediction to reduce or removeredundancy inherent in video sequences. For block-based video coding, avideo slice (e.g., a video frame, a portion of a video frame, etc.) maybe partitioned into video blocks, which may also be referred to astreeblocks, coding units (CUs) and/or coding nodes. Video blocks in anintra-coded (I) slice of a picture are encoded using spatial predictionwith respect to reference samples in neighboring blocks in the samepicture. Video blocks in an inter-coded (P or B) slice of a picture mayuse spatial prediction with respect to reference samples in neighboringblocks in the same picture or temporal prediction with respect toreference samples in other reference pictures. Pictures may be referredto as frames, and reference pictures may be referred to as referenceframes.

Spatial or temporal prediction results in a predictive block for a blockto be coded. Residual data represents pixel differences between theoriginal block to be coded and the predictive block. An inter-codedblock is encoded according to a motion vector that points to a block ofreference samples forming the predictive block, and the residual dataindicating the difference between the coded block and the predictiveblock. An intra-coded block is encoded according to an intra-coding modeand the residual data. For further compression, the residual data may betransformed from the pixel domain to a transform domain, resulting inresidual transform coefficients, which then may be quantized. Thequantized transform coefficients, initially arranged in atwo-dimensional array, may be scanned in order to produce aone-dimensional vector of transform coefficients, and entropy encodingmay be applied to achieve even more compression.

SUMMARY

Scalable video coding (SVC) refers to video coding in which a base layer(BL), sometimes referred to as a reference layer (RL), and one or morescalable enhancement layers (ELs) are used. In SVC, the base layer cancarry video data with a base level of quality. The one or moreenhancement layers can carry additional video data to support, forexample, higher spatial, temporal, and/or signal-to-noise (SNR) levels.Enhancement layers may be defined relative to a previously encodedlayer. For example, a bottom layer may serve as a BL, while a top layermay serve as an EL. Middle layers may serve as either ELs or RLs, orboth. For example, a middle layer (e.g., a layer that is neither thelowest layer nor the highest layer) may be an EL for the layers belowthe middle layer, such as the base layer or any intervening enhancementlayers, and at the same time serve as a RL for one or more enhancementlayers above the middle layer. Similarly, in the Multiview or 3Dextension of the HEVC standard, there may be multiple views, andinformation of one view may be utilized to code (e.g., encode or decode)the information of another view (e.g., motion estimation, motion vectorprediction and/or other redundancies).

In SVC, a picture order count (POC) may be used to indicate the order inwhich the pictures are to be output or displayed. Further, in someimplementations, the value of the POC may be reset (e.g., set to zero,set to some value signaled in the bitstream, or derived from informationincluded in the bitstream) whenever certain types of pictures appear inthe bitstream. For example, when certain random access point picturesappear in the bitstream, the POC may be reset. When the POC of aparticular picture is reset, the POCs of any pictures that precede theparticular picture in decoding order may also be reset, for example, tomaintain the relative order in which those pictures are to be output ordisplayed.

Such a POC reset may produce an undesired outcome when the TRAP picturesare not required to be aligned across different layers. For example,when one picture (“picA”) is an TRAP picture and another picture(“picB”) in the same access unit is not an TRAP picture, the POC valueof a picture (“picC”) that precedes picA in the same layer may bedifferent from the POC value of a picture (“picD”) that precedes picB inthe same layer and is in the same access unit as picC, because the POCvalue of picC is reset due to picA being an TRAP picture while the POCvalue of picD is not reset. This causes picC and picD, which are in thesame access unit and thus should have the same POC values, to havedifferent POC values.

Thus, an improved coding method for deriving the POC values when randomaccess pictures are not aligned across multiple layers is desired.

The systems, methods and devices of this disclosure each have severalinnovative aspects, no single one of which is solely responsible for thedesirable attributes disclosed herein.

In one aspect, an apparatus configured to code (e.g., encode or decode)video information includes a memory unit and a processor incommunication with the memory unit. The memory unit is configured tostore video information associated with a first video layer having afirst picture. The processor is configured to process picture ordercount (POC) derivation information associated with the first picture,and determine, based on the POC derivation information associated withthe first picture, a POC value of at least one other picture in thefirst video layer that precedes the first picture in decoding order.

In another aspect, a method of coding video information comprisesprocessing picture order count (POC) derivation information associatedwith a first picture in a first video layer, and determining, based onthe POC derivation information associated with the first picture, a POCvalue of at least one other picture in the first video layer thatprecedes the first picture in decoding order.

In another aspect, a non-transitory computer readable medium comprisescode that, when executed, causes an apparatus to perform a process. Theprocess includes storing video information associated with a first videolayer having a first picture, processing picture order count (POC)derivation information associated with the first picture, anddetermining, based on the POC derivation information associated with thefirst picture, a POC value of at least one other picture in the firstvideo layer that precedes the first picture in decoding order.

In another aspect, a video coding device configured to code videoinformation comprises means for storing video information associatedwith a first video layer having a first picture, means for processingpicture order count (POC) derivation information associated with thefirst picture, and means for determining, based on the POC derivationinformation associated with the first picture, a POC value of at leastone other picture in the first video layer that precedes the firstpicture in decoding order.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a block diagram illustrating an example video encoding anddecoding system that may utilize techniques in accordance with aspectsdescribed in this disclosure.

FIG. 1B is a block diagram illustrating another example video encodingand decoding system that may perform techniques in accordance withaspects described in this disclosure.

FIG. 2A is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 2B is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 3A is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 3B is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure.

FIG. 4 is a block diagram illustrating an example configuration ofpictures in different layers, according to one embodiment of the presentdisclosure.

FIG. 5 is a table illustrating POC values of pictures in differentlayers, according to one embodiment of the present disclosure.

FIG. 6 is a block diagram illustrating an example configuration ofpictures in different layers, according to one embodiment of the presentdisclosure.

FIG. 7 is a table illustrating POC values of pictures in differentlayers, according to one embodiment of the present disclosure.

FIG. 8 is a flow chart illustrating a method of coding videoinformation, according to one embodiment of the present disclosure.

FIG. 9 is a flow chart illustrating a method of coding videoinformation, according to one embodiment of the present disclosure.

FIG. 10 is a flow chart illustrating a method of coding videoinformation, according to one embodiment of the present disclosure.

FIG. 11 is a flow chart illustrating a method of coding videoinformation, according to one embodiment of the present disclosure.

FIG. 12 is a flow chart illustrating a method of coding videoinformation, according to one embodiment of the present disclosure.

DETAILED DESCRIPTION

Certain embodiments described herein relate to inter-layer predictionfor scalable video coding in the context of advanced video codecs, suchas HEVC (High Efficiency Video Coding). More specifically, the presentdisclosure relates to systems and methods for improved performance ofinter-layer prediction in scalable video coding (SVC) extension of HEVC.

In the description below, H.264/AVC techniques related to certainembodiments are described; the HEVC standard and related techniques arealso discussed. While certain embodiments are described herein in thecontext of the HEVC and/or H.264 standards, one having ordinary skill inthe art may appreciate that systems and methods disclosed herein may beapplicable to any suitable video coding standard. For example,embodiments disclosed herein may be applicable to one or more of thefollowing standards: ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-T H.262 orISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual and ITU-TH.264 (also known as ISO/IEC MPEG-4 AVC), including its Scalable VideoCoding (SVC) and Multiview Video Coding (MVC) extensions.

HEVC generally follows the framework of previous video coding standardsin many respects. The unit of prediction in HEVC is different from thatin certain previous video coding standards (e.g., macroblock). In fact,the concept of macroblock does not exist in HEVC as understood incertain previous video coding standards. Macroblock is replaced by ahierarchical structure based on a quadtree scheme, which may providehigh flexibility, among other possible benefits. For example, within theHEVC scheme, three types of blocks, Coding Unit (CU), Prediction Unit(PU), and Transform Unit (TU), are defined. CU may refer to the basicunit of region splitting. CU may be considered analogous to the conceptof macroblock, but HEVC does not restrict the maximum size of CUs andmay allow recursive splitting into four equal size CUs to improve thecontent adaptivity. PU may be considered the basic unit of inter/intraprediction, and a single PU may contain multiple arbitrary shapepartitions to effectively code irregular image patterns. TU may beconsidered the basic unit of transform. TU can be defined independentlyfrom the PU; however, the size of a TU may be limited to the size of theCU to which the TU belongs. This separation of the block structure intothree different concepts may allow each unit to be optimized accordingto the respective role of the unit, which may result in improved codingefficiency.

For purposes of illustration only, certain embodiments disclosed hereinare described with examples including only two layers (e.g., a lowerlayer such as the base layer, and a higher layer such as the enhancementlayer). It should be understood that such examples may be applicable toconfigurations including multiple base and/or enhancement layers. Inaddition, for ease of explanation, the following disclosure includes theterms “frames” or “blocks” with reference to certain embodiments.However, these terms are not meant to be limiting. For example, thetechniques described below can be used with any suitable video units,such as blocks (e.g., CU, PU, TU, macroblocks, etc.), slices, frames,etc.

Video Coding Standards

A digital image, such as a video image, a TV image, a still image or animage generated by a video recorder or a computer, may consist of pixelsor samples arranged in horizontal and vertical lines. The number ofpixels in a single image is typically in the tens of thousands. Eachpixel typically contains luminance and chrominance information. Withoutcompression, the sheer quantity of information to be conveyed from animage encoder to an image decoder would render real-time imagetransmission impossible. To reduce the amount of information to betransmitted, a number of different compression methods, such as JPEG,MPEG and H.263 standards, have been developed.

Video coding standards include ITU-T H.261, ISO/IEC MPEG-1 Visual, ITU-TH.262 or ISO/IEC MPEG-2 Visual, ITU-T H.263, ISO/IEC MPEG-4 Visual andITU-T H.264 (also known as ISO/IEC MPEG-4 AVC), including its ScalableVideo Coding (SVC) and Multiview Video Coding (MVC) extensions.

In addition, a new video coding standard, namely High Efficiency VideoCoding (HEVC), is being developed by the Joint Collaboration Team onVideo Coding (JCT-VC) of ITU-T Video Coding Experts Group (VCEG) andISO/IEC Motion Picture Experts Group (MPEG). The full citation for theHEVC Draft 10 is document JCTVC-L1003, Bross et al., “High EfficiencyVideo Coding (HEVC) Text Specification Draft 10,” Joint CollaborativeTeam on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IECJTC1/SC29/WG11, 12th Meeting: Geneva, Switzerland, Jan. 14, 2013 to Jan.23, 2013. The multiview extension to HEVC, namely MV-HEVC, and thescalable extension to HEVC, named SHVC, are also being developed by theJCT-3V (ITU-T/ISO/IEC Joint Collaborative Team on 3D Video CodingExtension Development) and JCT-VC, respectively.

Various aspects of the novel systems, apparatuses, and methods aredescribed more fully hereinafter with reference to the accompanyingdrawings. This disclosure may, however, be embodied in many differentforms and should not be construed as limited to any specific structureor function presented throughout this disclosure. Rather, these aspectsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the disclosure to those skilled in theart. Based on the teachings herein one skilled in the art shouldappreciate that the scope of the disclosure is intended to cover anyaspect of the novel systems, apparatuses, and methods disclosed herein,whether implemented independently of, or combined with, any other aspectof the present disclosure. For example, an apparatus may be implementedor a method may be practiced using any number of the aspects set forthherein. In addition, the scope of the present disclosure is intended tocover such an apparatus or method which is practiced using otherstructure, functionality, or structure and functionality in addition toor other than the various aspects of the present disclosure set forthherein. It should be understood that any aspect disclosed herein may beembodied by one or more elements of a claim.

Although particular aspects are described herein, many variations andpermutations of these aspects fall within the scope of the disclosure.Although some benefits and advantages of the preferred aspects arementioned, the scope of the disclosure is not intended to be limited toparticular benefits, uses, or objectives. Rather, aspects of thedisclosure are intended to be broadly applicable to different wirelesstechnologies, system configurations, networks, and transmissionprotocols, some of which are illustrated by way of example in thefigures and in the following description of the preferred aspects. Thedetailed description and drawings are merely illustrative of thedisclosure rather than limiting, the scope of the disclosure beingdefined by the appended claims and equivalents thereof.

The attached drawings illustrate examples. Elements indicated byreference numbers in the attached drawings correspond to elementsindicated by like reference numbers in the following description. Inthis disclosure, elements having names that start with ordinal words(e.g., “first,” “second,” “third,” and so on) do not necessarily implythat the elements have a particular order. Rather, such ordinal wordsare merely used to refer to different elements of a same or similartype.

Video Coding System

FIG. 1A is a block diagram that illustrates an example video codingsystem 10 that may utilize techniques in accordance with aspectsdescribed in this disclosure. As used described herein, the term “videocoder” refers generically to both video encoders and video decoders. Inthis disclosure, the terms “video coding” or “coding” may refergenerically to video encoding and video decoding. In addition to videoencoders and video decoders, the aspects described in the presentapplication may be extended to other related devices such as transcoders(e.g., devices that can decode a bitstream and re-encode anotherbitstream) and middleboxes (e.g., devices that can modify, transform,and/or otherwise manipulate a bitstream).

As shown in FIG. 1A, video coding system 10 includes a source module 12that generates encoded video data to be decoded at a later time by adestination module 14. In the example of FIG. 1A, the source module 12and destination module 14 are on separate devices—specifically, thesource module 12 is part of a source device, and the destination module14 is part of a destination device. It is noted, however, that thesource and destination modules 12, 14 may be on or part of the samedevice, as shown in the example of FIG. 1B.

With reference once again, to FIG. 1A, the source module 12 and thedestination module 14 may comprise any of a wide range of devices,including desktop computers, notebook (e.g., laptop) computers, tabletcomputers, set-top boxes, telephone handsets such as so-called “smart”phones, so-called “smart” pads, televisions, cameras, display devices,digital media players, video gaming consoles, video streaming device, orthe like. In some cases, the source module 12 and the destination module14 may be equipped for wireless communication.

The destination module 14 may receive the encoded video data to bedecoded via a link 16. The link 16 may comprise any type of medium ordevice capable of moving the encoded video data from the source module12 to the destination module 14. In the example of FIG. IA, the link 16may comprise a communication medium to enable the source module 12 totransmit encoded video data directly to the destination module 14 inreal-time. The encoded video data may be modulated according to acommunication standard, such as a wireless communication protocol, andtransmitted to the destination module 14. The communication medium maycomprise any wireless or wired communication medium, such as a radiofrequency (RF) spectrum or one or more physical transmission lines. Thecommunication medium may form part of a packet-based network, such as alocal area network, a wide-area network, or a global network such as theInternet. The communication medium may include routers, switches, basestations, or any other equipment that may be useful to facilitatecommunication from the source module 12 to the destination module 14.

Alternatively, encoded data may be output from an output interface 22 toan optional storage device 31. Similarly, encoded data may be accessedfrom the storage device 31 by an input interface 28. The storage device31 may include any of a variety of distributed or locally accessed datastorage media such as a hard drive, flash memory, volatile ornon-volatile memory, or any other suitable digital storage media forstoring encoded video data. In a further example, the storage device 31may correspond to a file server or another intermediate storage devicethat may hold the encoded video generated by the source module 12. Thedestination module 14 may access stored video data from the storagedevice 31 via streaming or download. The file server may be any type ofserver capable of storing encoded video data and transmitting thatencoded video data to the destination module 14. Example file serversinclude a web server (e.g., for a website), an FTP server, networkattached storage (NAS) devices, or a local disk drive. The destinationmodule 14 may access the encoded video data through any standard dataconnection, including an Internet connection. This may include awireless channel (e.g., a Wi-Fi connection), a wired connection (e.g.,DSL, cable modem, etc.), or a combination of both that is suitable foraccessing encoded video data stored on a file server. The transmissionof encoded video data from the storage device 31 may be a streamingtransmission, a download transmission, or a combination of both.

The techniques of this disclosure are not limited to wirelessapplications or settings. The techniques may be applied to video codingin support of any of a variety of multimedia applications, such asover-the-air television broadcasts, cable television transmissions,satellite television transmissions, streaming video transmissions, e.g.,via the Internet (e.g., dynamic adaptive streaming over HTTP (DASH),etc.), encoding of digital video for storage on a data storage medium,decoding of digital video stored on a data storage medium, or otherapplications. In some examples, video coding system 10 may be configuredto support one-way or two-way video transmission to support applicationssuch as video streaming, video playback, video broadcasting, and/orvideo telephony.

In the example of FIG. 1A, the source module 12 includes a video source18, video encoder 20 and an output interface 22. In some cases, theoutput interface 22 may include a modulator/demodulator (modem) and/or atransmitter. In the source module 12, the video source 18 may include asource such as a video capture device, e.g., a video camera, a videoarchive containing previously captured video, a video feed interface toreceive video from a video content provider, and/or a computer graphicssystem for generating computer graphics data as the source video, or acombination of such sources. As one example, if the video source 18 is avideo camera, the source module 12 and the destination module 14 mayform so-called camera phones or video phones, as illustrated in theexample of FIG. 1B. However, the techniques described in this disclosuremay be applicable to video coding in general, and may be applied towireless and/or wired applications.

The captured, pre-captured, or computer-generated video may be encodedby the video encoder 20. The encoded video data may be transmitteddirectly to the destination module 14 via the output interface 22 of thesource module 12. The encoded video data may also (or alternatively) bestored onto the storage device 31 for later access by the destinationmodule 14 or other devices, for decoding and/or playback. The videoencoder 20 illustrated in FIGS. 1A and 1B may comprise the video encoder20 illustrated FIG. 2A, the video encoder 23 illustrated in FIG. 2B, orany other video encoder described herein.

In the example of FIG. 1A, the destination module 14 includes an inputinterface 28, a video decoder 30, and a display device 32. In somecases, the input interface 28 may include a receiver and/or a modem. Theinput interface 28 of the destination module 14 may receive the encodedvideo data over the link 16. The encoded video data communicated overthe link 16, or provided on the storage device 31, may include a varietyof syntax elements generated by the video encoder 20 for use by a videodecoder, such as the video decoder 30, in decoding the video data. Suchsyntax elements may be included with the encoded video data transmittedon a communication medium, stored on a storage medium, or stored a fileserver. The video decoder 30 illustrated in FIGS. 1A and 1B may comprisethe video decoder 30 illustrated FIG. 3A, the video decoder 33illustrated in FIG. 3B, or any other video decoder described herein.

The display device 32 may be integrated with, or external to, thedestination module 14. In some examples, the destination module 14 mayinclude an integrated display device and also be configured to interfacewith an external display device. In other examples, the destinationmodule 14 may be a display device. In general, the display device 32displays the decoded video data to a user, and may comprise any of avariety of display devices such as a liquid crystal display (LCD), aplasma display, an organic light emitting diode (OLED) display, oranother type of display device.

In related aspects, FIG. 1B shows an example video encoding and decodingsystem 10′ wherein the source and destination modules 12, 14 are on orpart of a device or user device 11. The device 11 may be a telephonehandset, such as a “smart” phone or the like. The device 11 may includean optional controller/processor module 13 in operative communicationwith the source and destination modules 12, 14. The system 10′ of FIG.1B may further include a video processing unit 21 between the videoencoder 20 and the output interface 22. In some implementations, thevideo processing unit 21 is a separate unit, as illustrated in FIG. 1B;however, in other implementations, the video processing unit 21 can beimplemented as a portion of the video encoder 20 and/or theprocessor/controller module 13. The system 10′ may also include anoptional tracker 29, which can track an object of interest in a videosequence. The object or interest to be tracked may be segmented by atechnique described in connection with one or more aspects of thepresent disclosure. In related aspects, the tracking may be performed bythe display device 32, alone or in conjunction with the tracker 29. Thesystem 10′ of FIG. 1B, and components thereof, are otherwise similar tothe system 10 of FIG. 1A, and components thereof.

Video encoder 20 and video decoder 30 may operate according to a videocompression standard, such as the High Efficiency Video Coding (HEVC)standard presently under development, and may conform to a HEVC TestModel (HM). Alternatively, video encoder 20 and video decoder 30 mayoperate according to other proprietary or industry standards, such asthe ITU-T H.264 standard, alternatively referred to as MPEG-4, Part 10,Advanced Video Coding (AVC), or extensions of such standards. Thetechniques of this disclosure, however, are not limited to anyparticular coding standard. Other examples of video compressionstandards include MPEG-2 and ITU-T H.263.

Although not shown in the examples of FIGS. 1A and 1B, video encoder 20and video decoder 30 may each be integrated with an audio encoder anddecoder, and may include appropriate MUX-DEMUX units, or other hardwareand software, to handle encoding of both audio and video in a commondata stream or separate data streams. If applicable, in some examples,MUX-DEMUX units may conform to the ITU H.223 multiplexer protocol, orother protocols such as the user datagram protocol (UDP).

The video encoder 20 and the video decoder 30 each may be implemented asany of a variety of suitable encoder circuitry, such as one or moremicroprocessors, digital signal processors (DSPs), application specificintegrated circuits (ASICs), field programmable gate arrays (FPGAs),discrete logic, software, hardware, firmware or any combinationsthereof. When the techniques are implemented partially in software, adevice may store instructions for the software in a suitable,non-transitory computer-readable medium and execute the instructions inhardware using one or more processors to perform the techniques of thisdisclosure. Each of the video encoder 20 and the video decoder 30 may beincluded in one or more encoders or decoders, either of which may beintegrated as part of a combined encoder/decoder (CODEC) in a respectivedevice.

Video Coding Process

As mentioned briefly above, video encoder 20 encodes video data. Thevideo data may comprise one or more pictures. Each of the pictures is astill image forming part of a video. In some instances, a picture may bereferred to as a video “frame.” When video encoder 20 encodes the videodata, video encoder 20 may generate a bitstream. The bitstream mayinclude a sequence of bits that form a coded representation of the videodata. The bitstream may include coded pictures and associated data. Acoded picture is a coded representation of a picture.

To generate the bitstream, video encoder 20 may perform encodingoperations on each picture in the video data. When video encoder 20performs encoding operations on the pictures, video encoder 20 maygenerate a series of coded pictures and associated data. The associateddata may include video parameter sets (VPS), sequence parameter sets,picture parameter sets, adaptation parameter sets, and other syntaxstructures. A sequence parameter set (SPS) may contain parametersapplicable to zero or more sequences of pictures. A picture parameterset (PPS) may contain parameters applicable to zero or more pictures. Anadaptation parameter set (APS) may contain parameters applicable to zeroor more pictures. Parameters in an APS may be parameters that are morelikely to change than parameters in a PPS.

To generate a coded picture, video encoder 20 may partition a pictureinto equally-sized video blocks. A video block may be a two-dimensionalarray of samples. Each of the video blocks is associated with atreeblock. In some instances, a treeblock may be referred to as alargest coding unit (LCU). The treeblocks of HEVC may be broadlyanalogous to the macroblocks of previous standards, such as H.264/AVC.However, a treeblock is not necessarily limited to a particular size andmay include one or more coding units (CUs). Video encoder 20 may usequadtree partitioning to partition the video blocks of treeblocks intovideo blocks associated with CUs, hence the name “treeblocks.”

In some examples, video encoder 20 may partition a picture into aplurality of slices. Each of the slices may include an integer number ofCUs. In some instances, a slice comprises an integer number oftreeblocks. In other instances, a boundary of a slice may be within atreeblock.

As part of performing an encoding operation on a picture, video encoder20 may perform encoding operations on each slice of the picture. Whenvideo encoder 20 performs an encoding operation on a slice, videoencoder 20 may generate encoded data associated with the slice. Theencoded data associated with the slice may be referred to as a “codedslice.”

To generate a coded slice, video encoder 20 may perform encodingoperations on each treeblock in a slice. When video encoder 20 performsan encoding operation on a treeblock, video encoder 20 may generate acoded treeblock. The coded treeblock may comprise data representing anencoded version of the treeblock.

When video encoder 20 generates a coded slice, video encoder 20 mayperform encoding operations on (e.g., encode) the treeblocks in theslice according to a raster scan order. For example, video encoder 20may encode the treeblocks of the slice in an order that proceeds fromleft to right across a topmost row of treeblocks in the slice, then fromleft to right across a next lower row of treeblocks, and so on untilvideo encoder 20 has encoded each of the treeblocks in the slice.

As a result of encoding the treeblocks according to the raster scanorder, the treeblocks above and to the left of a given treeblock mayhave been encoded, but treeblocks below and to the right of the giventreeblock have not yet been encoded. Consequently, video encoder 20 maybe able to access information generated by encoding treeblocks above andto the left of the given treeblock when encoding the given treeblock.However, video encoder 20 may be unable to access information generatedby encoding treeblocks below and to the right of the given treeblockwhen encoding the given treeblock.

To generate a coded treeblock, video encoder 20 may recursively performquadtree partitioning on the video block of the treeblock to divide thevideo block into progressively smaller video blocks. Each of the smallervideo blocks may be associated with a different CU. For example, videoencoder 20 may partition the video block of a treeblock into fourequally-sized sub-blocks, partition one or more of the sub-blocks intofour equally-sized sub-sub-blocks, and so on. A partitioned CU may be aCU whose video block is partitioned into video blocks associated withother CUs. A non-partitioned CU may be a CU whose video block is notpartitioned into video blocks associated with other CUs.

One or more syntax elements in the bitstream may indicate a maximumnumber of times video encoder 20 may partition the video block of atreeblock. A video block of a CU may be square in shape. The size of thevideo block of a CU (e.g., the size of the CU) may range from 8×8 pixelsup to the size of a video block of a treeblock (e.g., the size of thetreeblock) with a maximum of 64×64 pixels or greater.

Video encoder 20 may perform encoding operations on (e.g., encode) eachCU of a treeblock according to a z-scan order. In other words, videoencoder 20 may encode a top-left CU, a top-right CU, a bottom-left CU,and then a bottom-right CU, in that order. When video encoder 20performs an encoding operation on a partitioned CU, video encoder 20 mayencode CUs associated with sub-blocks of the video block of thepartitioned CU according to the z-scan order. In other words, videoencoder 20 may encode a CU associated with a top-left sub-block, a CUassociated with a top-right sub-block, a CU associated with abottom-left sub-block, and then a CU associated with a bottom-rightsub-block, in that order.

As a result of encoding the CUs of a treeblock according to a z-scanorder, the CUs above, above-and-to-the-left, above-and-to-the-right,left, and below-and-to-the left of a given CU may have been encoded. CUsbelow and to the right of the given CU have not yet been encoded.Consequently, video encoder 20 may be able to access informationgenerated by encoding some CUs that neighbor the given CU when encodingthe given CU. However, video encoder 20 may be unable to accessinformation generated by encoding other CUs that neighbor the given CUwhen encoding the given CU.

When video encoder 20 encodes a non-partitioned CU, video encoder 20 maygenerate one or more prediction units (PUs) for the CU. Each of the PUsof the CU may be associated with a different video block within thevideo block of the CU. Video encoder 20 may generate a predicted videoblock for each PU of the CU. The predicted video block of a PU may be ablock of samples. Video encoder 20 may use intra prediction or interprediction to generate the predicted video block for a PU.

When video encoder 20 uses intra prediction to generate the predictedvideo block of a PU, video encoder 20 may generate the predicted videoblock of the PU based on decoded samples of the picture associated withthe PU. If video encoder 20 uses intra prediction to generate predictedvideo blocks of the PUs of a CU, the CU is an intra-predicted CU. Whenvideo encoder 20 uses inter prediction to generate the predicted videoblock of the PU, video encoder 20 may generate the predicted video blockof the PU based on decoded samples of one or more pictures other thanthe picture associated with the PU. If video encoder 20 uses interprediction to generate predicted video blocks of the PUs of a CU, the CUis an inter-predicted CU.

Furthermore, when video encoder 20 uses inter prediction to generate apredicted video block for a PU, video encoder 20 may generate motioninformation for the PU. The motion information for a PU may indicate oneor more reference blocks of the PU. Each reference block of the PU maybe a video block within a reference picture. The reference picture maybe a picture other than the picture associated with the PU. In someinstances, a reference block of a PU may also be referred to as the“reference sample” of the PU. Video encoder 20 may generate thepredicted video block for the PU based on the reference blocks of thePU.

After video encoder 20 generates predicted video blocks for one or morePUs of a CU, video encoder 20 may generate residual data for the CUbased on the predicted video blocks for the PUs of the CU. The residualdata for the CU may indicate differences between samples in thepredicted video blocks for the PUs of the CU and the original videoblock of the CU.

Furthermore, as part of performing an encoding operation on anon-partitioned CU, video encoder 20 may perform recursive quadtreepartitioning on the residual data of the CU to partition the residualdata of the CU into one or more blocks of residual data (e.g., residualvideo blocks) associated with transform units (TUs) of the CU. Each TUof a CU may be associated with a different residual video block.

Video encoder 20 may apply one or more transforms to residual videoblocks associated with the TUs to generate transform coefficient blocks(e.g., blocks of transform coefficients) associated with the TUs.Conceptually, a transform coefficient block may be a two-dimensional(2D) matrix of transform coefficients.

After generating a transform coefficient block, video encoder 20 mayperform a quantization process on the transform coefficient block.Quantization generally refers to a process in which transformcoefficients are quantized to possibly reduce the amount of data used torepresent the transform coefficients, providing further compression. Thequantization process may reduce the bit depth associated with some orall of the transform coefficients. For example, an n-bit transformcoefficient may be rounded down to an m-bit transform coefficient duringquantization, where n is greater than m.

Video encoder 20 may associate each CU with a quantization parameter(QP) value. The QP value associated with a CU may determine how videoencoder 20 quantizes transform coefficient blocks associated with theCU. Video encoder 20 may adjust the degree of quantization applied tothe transform coefficient blocks associated with a CU by adjusting theQP value associated with the CU.

After video encoder 20 quantizes a transform coefficient block, videoencoder 20 may generate sets of syntax elements that represent thetransform coefficients in the quantized transform coefficient block.Video encoder 20 may apply entropy encoding operations, such as ContextAdaptive Binary Arithmetic Coding (CABAC) operations, to some of thesesyntax elements. Other entropy coding techniques such as contentadaptive variable length coding (CAVLC), probability intervalpartitioning entropy (PIPE) coding, or other binary arithmetic codingcould also be used.

The bitstream generated by video encoder 20 may include a series ofNetwork Abstraction Layer (NAL) units. Each of the NAL units may be asyntax structure containing an indication of a type of data in the NALunit and bytes containing the data. For example, a NAL unit may containdata representing a video parameter set, a sequence parameter set, apicture parameter set, a coded slice, supplemental enhancementinformation (SEI), an access unit delimiter, filler data, or anothertype of data. The data in a NAL unit may include various syntaxstructures.

Video decoder 30 may receive the bitstream generated by video encoder20. The bitstream may include a coded representation of the video dataencoded by video encoder 20. When video decoder 30 receives thebitstream, video decoder 30 may perform a parsing operation on thebitstream. When video decoder 30 performs the parsing operation, videodecoder 30 may extract syntax elements from the bitstream. Video decoder30 may reconstruct the pictures of the video data based on the syntaxelements extracted from the bitstream. The process to reconstruct thevideo data based on the syntax elements may be generally reciprocal tothe process performed by video encoder 20 to generate the syntaxelements.

After video decoder 30 extracts the syntax elements associated with aCU, video decoder 30 may generate predicted video blocks for the PUs ofthe CU based on the syntax elements. In addition, video decoder 30 mayinverse quantize transform coefficient blocks associated with TUs of theCU. Video decoder 30 may perform inverse transforms on the transformcoefficient blocks to reconstruct residual video blocks associated withthe TUs of the CU. After generating the predicted video blocks andreconstructing the residual video blocks, video decoder 30 mayreconstruct the video block of the CU based on the predicted videoblocks and the residual video blocks. In this way, video decoder 30 mayreconstruct the video blocks of CUs based on the syntax elements in thebitstream.

Video Encoder

FIG. 2A is a block diagram illustrating an example of a video encoderthat may implement techniques in accordance with aspects described inthis disclosure. Video encoder 20 may be configured to process a singlelayer of a video frame, such as for HEVC. Further, video encoder 20 maybe configured to perform any or all of the techniques of thisdisclosure. As one example, prediction processing unit 100 may beconfigured to perform any or all of the techniques described in thisdisclosure. In another embodiment, the video encoder 20 includes anoptional inter-layer prediction unit 128 that is configured to performany or all of the techniques described in this disclosure. In otherembodiments, inter-layer prediction can be performed by predictionprocessing unit 100 (e.g., inter prediction unit 121 and/or intraprediction unit 126), in which case the inter-layer prediction unit 128may be omitted. However, aspects of this disclosure are not so limited.In some examples, the techniques described in this disclosure may beshared among the various components of video encoder 20. In someexamples, additionally or alternatively, a processor (not shown) may beconfigured to perform any or all of the techniques described in thisdisclosure.

For purposes of explanation, this disclosure describes video encoder 20in the context of HEVC coding. However, the techniques of thisdisclosure may be applicable to other coding standards or methods. Theexample depicted in FIG. 2A is for a single layer codec. However, aswill be described further with respect to FIG. 2B, some or all of thevideo encoder 20 may be duplicated for processing of a multi-layercodec.

Video encoder 20 may perform intra- and inter-coding of video blockswithin video slices. Intra coding relies on spatial prediction to reduceor remove spatial redundancy in video within a given video frame orpicture. Inter-coding relies on temporal prediction to reduce or removetemporal redundancy in video within adjacent frames or pictures of avideo sequence. Intra-mode (I mode) may refer to any of several spatialbased coding modes. Inter-modes, such as uni-directional prediction (Pmode) or bi-directional prediction (B mode), may refer to any of severaltemporal-based coding modes.

In the example of FIG. 2A, video encoder 20 includes a plurality offunctional components. The functional components of video encoder 20include a prediction processing unit 100, a residual generation unit102, a transform processing unit 104, a quantization unit 106, aninverse quantization unit 108, an inverse transform unit 110, areconstruction unit 112, a filter unit 113, a decoded picture buffer114, and an entropy encoding unit 116. Prediction processing unit 100includes an inter prediction unit 121, a motion estimation unit 122, amotion compensation unit 124, an intra prediction unit 126, and aninter-layer prediction unit 128. In other examples, video encoder 20 mayinclude more, fewer, or different functional components. Furthermore,motion estimation unit 122 and motion compensation unit 124 may behighly integrated, but are represented in the example of FIG. 2Aseparately for purposes of explanation.

Video encoder 20 may receive video data. Video encoder 20 may receivethe video data from various sources. For example, video encoder 20 mayreceive the video data from video source 18 (e.g., shown in FIG. 1A or1B) or another source. The video data may represent a series ofpictures. To encode the video data, video encoder 20 may perform anencoding operation on each of the pictures. As part of performing theencoding operation on a picture, video encoder 20 may perform encodingoperations on each slice of the picture. As part of performing anencoding operation on a slice, video encoder 20 may perform encodingoperations on treeblocks in the slice.

As part of performing an encoding operation on a treeblock, predictionprocessing unit 100 may perform quadtree partitioning on the video blockof the treeblock to divide the video block into progressively smallervideo blocks. Each of the smaller video blocks may be associated with adifferent CU. For example, prediction processing unit 100 may partitiona video block of a treeblock into four equally-sized sub-blocks,partition one or more of the sub-blocks into four equally-sizedsub-sub-blocks, and so on.

The sizes of the video blocks associated with CUs may range from 8×8samples up to the size of the treeblock with a maximum of 64×64 samplesor greater. In this disclosure, “N×N” and “N by N” may be usedinterchangeably to refer to the sample dimensions of a video block interms of vertical and horizontal dimensions, e.g., 16×16 samples or 16by 16 samples. In general, a 16×16 video block has sixteen samples in avertical direction (y=16) and sixteen samples in a horizontal direction(x=16). Likewise, an N×N block generally has N samples in a verticaldirection and N samples in a horizontal direction, where N represents anonnegative integer value.

Furthermore, as part of performing the encoding operation on atreeblock, prediction processing unit 100 may generate a hierarchicalquadtree data structure for the treeblock. For example, a treeblock maycorrespond to a root node of the quadtree data structure. If predictionprocessing unit 100 partitions the video block of the treeblock intofour sub-blocks, the root node has four child nodes in the quadtree datastructure. Each of the child nodes corresponds to a CU associated withone of the sub-blocks. If prediction processing unit 100 partitions oneof the sub-blocks into four sub-sub-blocks, the node corresponding tothe CU associated with the sub-block may have four child nodes, each ofwhich corresponds to a CU associated with one of the sub-sub-blocks.

Each node of the quadtree data structure may contain syntax data (e.g.,syntax elements) for the corresponding treeblock or CU. For example, anode in the quadtree may include a split flag that indicates whether thevideo block of the CU corresponding to the node is partitioned (e.g.,split) into four sub-blocks. Syntax elements for a CU may be definedrecursively, and may depend on whether the video block of the CU issplit into sub-blocks. A CU whose video block is not partitioned maycorrespond to a leaf node in the quadtree data structure. A codedtreeblock may include data based on the quadtree data structure for acorresponding treeblock.

Video encoder 20 may perform encoding operations on each non-partitionedCU of a treeblock. When video encoder 20 performs an encoding operationon a non-partitioned CU, video encoder 20 generates data representing anencoded representation of the non-partitioned CU.

As part of performing an encoding operation on a CU, predictionprocessing unit 100 may partition the video block of the CU among one ormore PUs of the CU. Video encoder 20 and video decoder 30 may supportvarious PU sizes. Assuming that the size of a particular CU is 2N×2N,video encoder 20 and video decoder 30 may support PU sizes of 2N×2N orN×N, and inter-prediction in symmetric PU sizes of 2N×2N, 2N×N, N×2N,N×N, 2N×nU, nL×2N, nR×2N, or similar. Video encoder 20 and video decoder30 may also support asymmetric partitioning for PU sizes of 2N×nU,2N×nD, nL×2N, and nR×2N. In some examples, prediction processing unit100 may perform geometric partitioning to partition the video block of aCU among PUs of the CU along a boundary that does not meet the sides ofthe video block of the CU at right angles.

Inter prediction unit 121 may perform inter prediction on each PU of theCU. Inter prediction may provide temporal compression. To perform interprediction on a PU, motion estimation unit 122 may generate motioninformation for the PU. Motion compensation unit 124 may generate apredicted video block for the PU based the motion information anddecoded samples of pictures other than the picture associated with theCU (e.g., reference pictures). In this disclosure, a predicted videoblock generated by motion compensation unit 124 may be referred to as aninter-predicted video block.

Slices may be I slices, P slices, or B slices. Motion estimation unit122 and motion compensation unit 124 may perform different operationsfor a PU of a CU depending on whether the PU is in an I slice, a Pslice, or a B slice. In an I slice, all PUs are intra predicted. Hence,if the PU is in an I slice, motion estimation unit 122 and motioncompensation unit 124 do not perform inter prediction on the PU.

If the PU is in a P slice, the picture containing the PU is associatedwith a list of reference pictures referred to as “list 0.” Each of thereference pictures in list 0 contains samples that may be used for interprediction of other pictures. When motion estimation unit 122 performsthe motion estimation operation with regard to a PU in a P slice, motionestimation unit 122 may search the reference pictures in list 0 for areference block for the PU. The reference block of the PU may be a setof samples, e.g., a block of samples, that most closely corresponds tothe samples in the video block of the PU. Motion estimation unit 122 mayuse a variety of metrics to determine how closely a set of samples in areference picture corresponds to the samples in the video block of a PU.For example, motion estimation unit 122 may determine how closely a setof samples in a reference picture corresponds to the samples in thevideo block of a PU by sum of absolute difference (SAD), sum of squaredifference (SSD), or other difference metrics.

After identifying a reference block of a PU in a P slice, motionestimation unit 122 may generate a reference index that indicates thereference picture in list 0 containing the reference block and a motionvector that indicates a spatial displacement between the PU and thereference block. In various examples, motion estimation unit 122 maygenerate motion vectors to varying degrees of precision. For example,motion estimation unit 122 may generate motion vectors at one-quartersample precision, one-eighth sample precision, or other fractionalsample precision. In the case of fractional sample precision, referenceblock values may be interpolated from integer-position sample values inthe reference picture. Motion estimation unit 122 may output thereference index and the motion vector as the motion information of thePU. Motion compensation unit 124 may generate a predicted video block ofthe PU based on the reference block identified by the motion informationof the PU.

If the PU is in a B slice, the picture containing the PU may beassociated with two lists of reference pictures, referred to as “list 0”and “list 1.” In some examples, a picture containing a B slice may beassociated with a list combination that is a combination of list 0 andlist 1.

Furthermore, if the PU is in a B slice, motion estimation unit 122 mayperform uni-directional prediction or bi-directional prediction for thePU. When motion estimation unit 122 performs uni-directional predictionfor the PU, motion estimation unit 122 may search the reference picturesof list 0 or list 1 for a reference block for the PU. Motion estimationunit 122 may then generate a reference index that indicates thereference picture in list 0 or list 1 that contains the reference blockand a motion vector that indicates a spatial displacement between the PUand the reference block. Motion estimation unit 122 may output thereference index, a prediction direction indicator, and the motion vectoras the motion information of the PU. The prediction direction indicatormay indicate whether the reference index indicates a reference picturein list 0 or list 1. Motion compensation unit 124 may generate thepredicted video block of the PU based on the reference block indicatedby the motion information of the PU.

When motion estimation unit 122 performs bi-directional prediction for aPU, motion estimation unit 122 may search the reference pictures in list0 for a reference block for the PU and may also search the referencepictures in list 1 for another reference block for the PU. Motionestimation unit 122 may then generate reference indexes that indicatethe reference pictures in list 0 and list 1 containing the referenceblocks and motion vectors that indicate spatial displacements betweenthe reference blocks and the PU. Motion estimation unit 122 may outputthe reference indexes and the motion vectors of the PU as the motioninformation of the PU. Motion compensation unit 124 may generate thepredicted video block of the PU based on the reference blocks indicatedby the motion information of the PU.

In some instances, motion estimation unit 122 does not output a full setof motion information for a PU to entropy encoding unit 116. Rather,motion estimation unit 122 may signal the motion information of a PUwith reference to the motion information of another PU. For example,motion estimation unit 122 may determine that the motion information ofthe PU is sufficiently similar to the motion information of aneighboring PU. In this example, motion estimation unit 122 mayindicate, in a syntax structure associated with the PU, a value thatindicates to video decoder 30 that the PU has the same motioninformation as the neighboring PU. In another example, motion estimationunit 122 may identify, in a syntax structure associated with the PU, aneighboring PU and a motion vector difference (MVD). The motion vectordifference indicates a difference between the motion vector of the PUand the motion vector of the indicated neighboring PU. Video decoder 30may use the motion vector of the indicated neighboring PU and the motionvector difference to determine the motion vector of the PU. By referringto the motion information of a first PU when signaling the motioninformation of a second PU, video encoder 20 may be able to signal themotion information of the second PU using fewer bits.

As further discussed below with reference to FIGS. 8-12, the predictionprocessing unit 100 may be configured to code (e.g., encode or decode)the PU (or any other reference layer and/or enhancement layer blocks orvideo units) by performing the methods illustrated in FIGS. 8-12. Forexample, inter prediction unit 121 (e.g., via motion estimation unit 122and/or motion compensation unit 124), intra prediction unit 126, orinter-layer prediction unit 128 may be configured to perform the methodsillustrated in FIGS. 8-12, either together or separately.

As part of performing an encoding operation on a CU, intra predictionunit 126 may perform intra prediction on PUs of the CU. Intra predictionmay provide spatial compression. When intra prediction unit 126 performsintra prediction on a PU, intra prediction unit 126 may generateprediction data for the PU based on decoded samples of other PUs in thesame picture. The prediction data for the PU may include a predictedvideo block and various syntax elements. Intra prediction unit 126 mayperform intra prediction on PUs in I slices, P slices, and B slices.

To perform intra prediction on a PU, intra prediction unit 126 may usemultiple intra prediction modes to generate multiple sets of predictiondata for the PU. When intra prediction unit 126 uses an intra predictionmode to generate a set of prediction data for the PU, intra predictionunit 126 may extend samples from video blocks of neighboring PUs acrossthe video block of the PU in a direction and/or gradient associated withthe intra prediction mode. The neighboring PUs may be above, above andto the right, above and to the left, or to the left of the PU, assuminga left-to-right, top-to-bottom encoding order for PUs, CUs, andtreeblocks. Intra prediction unit 126 may use various numbers of intraprediction modes, e.g., 33 directional intra prediction modes, dependingon the size of the PU.

Prediction processing unit 100 may select the prediction data for a PUfrom among the prediction data generated by motion compensation unit 124for the PU or the prediction data generated by intra prediction unit 126for the PU. In some examples, prediction processing unit 100 selects theprediction data for the PU based on rate/distortion metrics of the setsof prediction data.

If prediction processing unit 100 selects prediction data generated byintra prediction unit 126, prediction processing unit 100 may signal theintra prediction mode that was used to generate the prediction data forthe PUs, e.g., the selected intra prediction mode. Prediction processingunit 100 may signal the selected intra prediction mode in various ways.For example, it may be probable that the selected intra prediction modeis the same as the intra prediction mode of a neighboring PU. In otherwords, the intra prediction mode of the neighboring PU may be the mostprobable mode for the current PU. Thus, prediction processing unit 100may generate a syntax element to indicate that the selected intraprediction mode is the same as the intra prediction mode of theneighboring PU.

As discussed above, the video encoder 20 may include inter-layerprediction unit 128. Inter-layer prediction unit 128 is configured topredict a current block (e.g., a current block in the EL) using one ormore different layers that are available in SVC (e.g., a base orreference layer). Such prediction may be referred to as inter-layerprediction. Inter-layer prediction unit 128 utilizes prediction methodsto reduce inter-layer redundancy, thereby improving coding efficiencyand reducing computational resource requirements. Some examples ofinter-layer prediction include inter-layer intra prediction, inter-layermotion prediction, and inter-layer residual prediction. Inter-layerintra prediction uses the reconstruction of co-located blocks in thebase layer to predict the current block in the enhancement layer.Inter-layer motion prediction uses motion information of the base layerto predict motion in the enhancement layer. Inter-layer residualprediction uses the residue of the base layer to predict the residue ofthe enhancement layer. Each of the inter-layer prediction schemes isdiscussed below in greater detail.

After prediction processing unit 100 selects the prediction data for PUsof a CU, residual generation unit 102 may generate residual data for theCU by subtracting (e.g., indicated by the minus sign) the predictedvideo blocks of the PUs of the CU from the video block of the CU. Theresidual data of a CU may include 2D residual video blocks thatcorrespond to different sample components of the samples in the videoblock of the CU. For example, the residual data may include a residualvideo block that corresponds to differences between luminance componentsof samples in the predicted video blocks of the PUs of the CU andluminance components of samples in the original video block of the CU.In addition, the residual data of the CU may include residual videoblocks that correspond to the differences between chrominance componentsof samples in the predicted video blocks of the PUs of the CU and thechrominance components of the samples in the original video block of theCU.

Prediction processing unit 100 may perform quadtree partitioning topartition the residual video blocks of a CU into sub-blocks. Eachundivided residual video block may be associated with a different TU ofthe CU. The sizes and positions of the residual video blocks associatedwith TUs of a CU may or may not be based on the sizes and positions ofvideo blocks associated with the PUs of the CU. A quadtree structureknown as a “residual quad tree” (RQT) may include nodes associated witheach of the residual video blocks. The TUs of a CU may correspond toleaf nodes of the RQT.

Transform processing unit 104 may generate one or more transformcoefficient blocks for each TU of a CU by applying one or moretransforms to a residual video block associated with the TU. Each of thetransform coefficient blocks may be a 2D matrix of transformcoefficients. Transform processing unit 104 may apply various transformsto the residual video block associated with a TU. For example, transformprocessing unit 104 may apply a discrete cosine transform (DCT), adirectional transform, or a conceptually similar transform to theresidual video block associated with a TU.

After transform processing unit 104 generates a transform coefficientblock associated with a TU, quantization unit 106 may quantize thetransform coefficients in the transform coefficient block. Quantizationunit 106 may quantize a transform coefficient block associated with a TUof a CU based on a QP value associated with the CU.

Video encoder 20 may associate a QP value with a CU in various ways. Forexample, video encoder 20 may perform a rate-distortion analysis on atreeblock associated with the CU. In the rate-distortion analysis, videoencoder 20 may generate multiple coded representations of the treeblockby performing an encoding operation multiple times on the treeblock.Video encoder 20 may associate different QP values with the CU whenvideo encoder 20 generates different encoded representations of thetreeblock. Video encoder 20 may signal that a given QP value isassociated with the CU when the given QP value is associated with the CUin a coded representation of the treeblock that has a lowest bitrate anddistortion metric.

Inverse quantization unit 108 and inverse transform unit 110 may applyinverse quantization and inverse transforms to the transform coefficientblock, respectively, to reconstruct a residual video block from thetransform coefficient block. Reconstruction unit 112 may add thereconstructed residual video block to corresponding samples from one ormore predicted video blocks generated by prediction processing unit 100to produce a reconstructed video block associated with a TU. Byreconstructing video blocks for each TU of a CU in this way, videoencoder 20 may reconstruct the video block of the CU.

After reconstruction unit 112 reconstructs the video block of a CU,filter unit 113 may perform a deblocking operation to reduce blockingartifacts in the video block associated with the CU. After performingthe one or more deblocking operations, filter unit 113 may store thereconstructed video block of the CU in decoded picture buffer 114.Motion estimation unit 122 and motion compensation unit 124 may use areference picture that contains the reconstructed video block to performinter prediction on PUs of subsequent pictures. In addition, intraprediction unit 126 may use reconstructed video blocks in decodedpicture buffer 114 to perform intra prediction on other PUs in the samepicture as the CU.

Entropy encoding unit 116 may receive data from other functionalcomponents of video encoder 20. For example, entropy encoding unit 116may receive transform coefficient blocks from quantization unit 106 andmay receive syntax elements from prediction processing unit 100. Whenentropy encoding unit 116 receives the data, entropy encoding unit 116may perform one or more entropy encoding operations to generate entropyencoded data. For example, video encoder 20 may perform a contextadaptive variable length coding (CAVLC) operation, a CABAC operation, avariable-to-variable (V2V) length coding operation, a syntax-basedcontext-adaptive binary arithmetic coding (SBAC) operation, aProbability Interval Partitioning Entropy (PIPE) coding operation, oranother type of entropy encoding operation on the data. Entropy encodingunit 116 may output a bitstream that includes the entropy encoded data.

As part of performing an entropy encoding operation on data, entropyencoding unit 116 may select a context model. If entropy encoding unit116 is performing a CABAC operation, the context model may indicateestimates of probabilities of particular bins having particular values.In the context of CABAC, the term “bin” is used to refer to a bit of abinarized version of a syntax element.

Multi-Layer Video Encoder

FIG. 2B is a block diagram illustrating an example of a multi-layervideo encoder 23 that may implement techniques in accordance withaspects described in this disclosure. The video encoder 23 may beconfigured to process multi-layer video frames, such as for SHVC andmultiview coding. Further, the video encoder 23 may be configured toperform any or all of the techniques of this disclosure.

The video encoder 23 includes a video encoder 20A and video encoder 20B,each of which may be configured as the video encoder 20 and may performthe functions described above with respect to the video encoder 20.Further, as indicated by the reuse of reference numbers, the videoencoders 20A and 20B may include at least some of the systems andsubsystems as the video encoder 20. Although the video encoder 23 isillustrated as including two video encoders 20A and 20B, the videoencoder 23 is not limited as such and may include any number of videoencoder 20 layers. In some embodiments, the video encoder 23 may includea video encoder 20 for each picture or frame in an access unit. Forexample, an access unit that includes five pictures may be processed orencoded by a video encoder that includes five encoder layers. In someembodiments, the video encoder 23 may include more encoder layers thanframes in an access unit. In some such cases, some of the video encoderlayers may be inactive when processing some access units.

In addition to the video encoders 20A and 20B, the video encoder 23 mayinclude an resampling unit 90. The resampling unit 90 may, in somecases, upsample a base layer of a received video frame to, for example,create an enhancement layer. The resampling unit 90 may upsampleparticular information associated with the received base layer of aframe, but not other information. For example, the resampling unit 90may up sample the spatial size or number of pixels of the base layer,but the number of slices or the picture order count may remain constant.In some cases, the resampling unit 90 may not process the received videoand/or may be optional. For example, in some cases, the predictionprocessing unit 100 may perform upsampling. In some embodiments, theresampling unit 90 is configured to upsample a layer and reorganize,redefine, modify, or adjust one or more slices to comply with a set ofslice boundary rules and/or raster scan rules. Although primarilydescribed as upsampling a base layer, or a lower layer in an accessunit, in some cases, the resampling unit 90 may downsample a layer. Forexample, if during streaming of a video bandwidth is reduced, a framemay be downsampled instead of upsampled.

The resampling unit 90 may be configured to receive a picture or frame(or picture information associated with the picture) from the decodedpicture buffer 114 of the lower layer encoder (e.g., the video encoder20A) and to upsample the picture (or the received picture information).This upsampled picture may then be provided to the prediction processingunit 100 of a higher layer encoder (e.g., the video encoder 20B)configured to encode a picture in the same access unit as the lowerlayer encoder. In some cases, the higher layer encoder is one layerremoved from the lower layer encoder. In other cases, there may be oneor more higher layer encoders between the layer 0 video encoder and thelayer 1 encoder of FIG. 2B.

In some cases, the resampling unit 90 may be omitted or bypassed. Insuch cases, the picture from the decoded picture buffer 114 of the videoencoder 20A may be provided directly, or at least without being providedto the resampling unit 90, to the prediction processing unit 100 of thevideo encoder 20B. For example, if video data provided to the videoencoder 20B and the reference picture from the decoded picture buffer114 of the video encoder 20A are of the same size or resolution, thereference picture may be provided to the video encoder 20B without anyresampling.

In some embodiments, the video encoder 23 downsamples video data to beprovided to the lower layer encoder using the downsampling unit 94before provided the video data to the video encoder 20A. Alternatively,the downsampling unit 94 may be a resampling unit 90 capable ofupsampling or downsampling the video data. In yet other embodiments, thedownsampling unit 94 may be omitted.

As illustrated in FIG. 2B, the video encoder 23 may further include amultiplexor 98, or mux. The mux 98 can output a combined bitstream fromthe video encoder 23. The combined bitstream may be created by taking abitstream from each of the video encoders 20A and 20B and alternatingwhich bitstream is output at a given time. While in some cases the bitsfrom the two (or more in the case of more than two video encoder layers)bitstreams may be alternated one bit at a time, in many cases thebitstreams are combined differently. For example, the output bitstreammay be created by alternating the selected bitstream one block at atime. In another example, the output bitstream may be created byoutputting a non-1:1 ratio of blocks from each of the video encoders 20Aand 20B. For instance, two blocks may be output from the video encoder20B for each block output from the video encoder 20A. In someembodiments, the output stream from the mux 98 may be preprogrammed. Inother embodiments, the mux 98 may combine the bitstreams from the videoencoders 20A, 20B based on a control signal received from a systemexternal to the video encoder 23, such as from a processor on a sourcedevice including the source module 12. The control signal may begenerated based on the resolution or bitrate of a video from the videosource 18, based on a bandwidth of the link 16, based on a subscriptionassociated with a user (e.g., a paid subscription versus a freesubscription), or based on any other factor for determining a resolutionoutput desired from the video encoder 23.

Video Decoder

FIG. 3A is a block diagram illustrating an example of a video decoderthat may implement techniques in accordance with aspects described inthis disclosure. The video decoder 30 may be configured to process asingle layer of a video frame, such as for HEVC. Further, video decoder30 may be configured to perform any or all of the techniques of thisdisclosure. As one example, motion compensation unit 162 and/or intraprediction unit 164 may be configured to perform any or all of thetechniques described in this disclosure. In one embodiment, videodecoder 30 may optionally include inter-layer prediction unit 166 thatis configured to perform any or all of the techniques described in thisdisclosure. In other embodiments, inter-layer prediction can beperformed by prediction processing unit 152 (e.g., motion compensationunit 162 and/or intra prediction unit 164), in which case theinter-layer prediction unit 166 may be omitted. However, aspects of thisdisclosure are not so limited. In some examples, the techniquesdescribed in this disclosure may be shared among the various componentsof video decoder 30. In some examples, additionally or alternatively, aprocessor (not shown) may be configured to perform any or all of thetechniques described in this disclosure.

For purposes of explanation, this disclosure describes video decoder 30in the context of HEVC coding. However, the techniques of thisdisclosure may be applicable to other coding standards or methods. Theexample depicted in FIG. 3A is for a single layer codec. However, aswill be described further with respect to FIG. 3B, some or all of thevideo decoder 30 may be duplicated for processing of a multi-layercodec.

In the example of FIG. 3A, video decoder 30 includes a plurality offunctional components. The functional components of video decoder 30include an entropy decoding unit 150, a prediction processing unit 152,an inverse quantization unit 154, an inverse transform unit 156, areconstruction unit 158, a filter unit 159, and a decoded picture buffer160. Prediction processing unit 152 includes a motion compensation unit162, an intra prediction unit 164, and an inter-layer prediction unit166. In some examples, video decoder 30 may perform a decoding passgenerally reciprocal to the encoding pass described with respect tovideo encoder 20 of FIG. 2A. In other examples, video decoder 30 mayinclude more, fewer, or different functional components.

Video decoder 30 may receive a bitstream that comprises encoded videodata. The bitstream may include a plurality of syntax elements. Whenvideo decoder 30 receives the bitstream, entropy decoding unit 150 mayperform a parsing operation on the bitstream. As a result of performingthe parsing operation on the bitstream, entropy decoding unit 150 mayextract syntax elements from the bitstream. As part of performing theparsing operation, entropy decoding unit 150 may entropy decode entropyencoded syntax elements in the bitstream. Prediction processing unit152, inverse quantization unit 154, inverse transform unit 156,reconstruction unit 158, and filter unit 159 may perform areconstruction operation that generates decoded video data based on thesyntax elements extracted from the bitstream.

As discussed above, the bitstream may comprise a series of NAL units.The NAL units of the bitstream may include video parameter set NALunits, sequence parameter set NAL units, picture parameter set NALunits, SEI NAL units, and so on. As part of performing the parsingoperation on the bitstream, entropy decoding unit 150 may performparsing operations that extract and entropy decode sequence parametersets from sequence parameter set NAL units, picture parameter sets frompicture parameter set NAL units, SEI data from SEI NAL units, and so on.

In addition, the NAL units of the bitstream may include coded slice NALunits. As part of performing the parsing operation on the bitstream,entropy decoding unit 150 may perform parsing operations that extractand entropy decode coded slices from the coded slice NAL units. Each ofthe coded slices may include a slice header and slice data. The sliceheader may contain syntax elements pertaining to a slice. The syntaxelements in the slice header may include a syntax element thatidentifies a picture parameter set associated with a picture thatcontains the slice. Entropy decoding unit 150 may perform entropydecoding operations, such as CABAC decoding operations, on syntaxelements in the coded slice header to recover the slice header.

As part of extracting the slice data from coded slice NAL units, entropydecoding unit 150 may perform parsing operations that extract syntaxelements from coded CUs in the slice data. The extracted syntax elementsmay include syntax elements associated with transform coefficientblocks. Entropy decoding unit 150 may then perform CABAC decodingoperations on some of the syntax elements.

After entropy decoding unit 150 performs a parsing operation on anon-partitioned CU, video decoder 30 may perform a reconstructionoperation on the non-partitioned CU. To perform the reconstructionoperation on a non-partitioned CU, video decoder 30 may perform areconstruction operation on each TU of the CU. By performing thereconstruction operation for each TU of the CU, video decoder 30 mayreconstruct a residual video block associated with the CU.

As part of performing a reconstruction operation on a TU, inversequantization unit 154 may inverse quantize, e.g., de-quantize, atransform coefficient block associated with the TU. Inverse quantizationunit 154 may inverse quantize the transform coefficient block in amanner similar to the inverse quantization processes proposed for HEVCor defined by the H.264 decoding standard. Inverse quantization unit 154may use a quantization parameter QP calculated by video encoder 20 for aCU of the transform coefficient block to determine a degree ofquantization and, likewise, a degree of inverse quantization for inversequantization unit 154 to apply.

After inverse quantization unit 154 inverse quantizes a transformcoefficient block, inverse transform unit 156 may generate a residualvideo block for the TU associated with the transform coefficient block.Inverse transform unit 156 may apply an inverse transform to thetransform coefficient block in order to generate the residual videoblock for the TU. For example, inverse transform unit 156 may apply aninverse DCT, an inverse integer transform, an inverse Karhunen-Loevetransform (KLT), an inverse rotational transform, an inverse directionaltransform, or another inverse transform to the transform coefficientblock. In some examples, inverse transform unit 156 may determine aninverse transform to apply to the transform coefficient block based onsignaling from video encoder 20. In such examples, inverse transformunit 156 may determine the inverse transform based on a signaledtransform at the root node of a quadtree for a treeblock associated withthe transform coefficient block. In other examples, inverse transformunit 156 may infer the inverse transform from one or more codingcharacteristics, such as block size, coding mode, or the like. In someexamples, inverse transform unit 156 may apply a cascaded inversetransform.

In some examples, motion compensation unit 162 may refine the predictedvideo block of a PU by performing interpolation based on interpolationfilters. Identifiers for interpolation filters to be used for motioncompensation with sub-sample precision may be included in the syntaxelements. Motion compensation unit 162 may use the same interpolationfilters used by video encoder 20 during generation of the predictedvideo block of the PU to calculate interpolated values for sub-integersamples of a reference block. Motion compensation unit 162 may determinethe interpolation filters used by video encoder 20 according to receivedsyntax information and use the interpolation filters to produce thepredicted video block.

As further discussed below with reference to FIGS. 8-12, the predictionprocessing unit 152 may code (e.g., encode or decode) the PU (or anyother reference layer and/or enhancement layer blocks or video units) byperforming the methods illustrated in FIGS. 8-12. For example, motioncompensation unit 162, intra prediction unit 164, or inter-layerprediction unit 166 may be configured to perform the methods illustratedin FIGS. 8-12, either together or separately.

If a PU is encoded using intra prediction, intra prediction unit 164 mayperform intra prediction to generate a predicted video block for the PU.For example, intra prediction unit 164 may determine an intra predictionmode for the PU based on syntax elements in the bitstream. The bitstreammay include syntax elements that intra prediction unit 164 may use todetermine the intra prediction mode of the PU.

In some instances, the syntax elements may indicate that intraprediction unit 164 is to use the intra prediction mode of another PU todetermine the intra prediction mode of the current PU. For example, itmay be probable that the intra prediction mode of the current PU is thesame as the intra prediction mode of a neighboring PU. In other words,the intra prediction mode of the neighboring PU may be the most probablemode for the current PU. Hence, in this example, the bitstream mayinclude a small syntax element that indicates that the intra predictionmode of the PU is the same as the intra prediction mode of theneighboring PU. Intra prediction unit 164 may then use the intraprediction mode to generate prediction data (e.g., predicted samples)for the PU based on the video blocks of spatially neighboring PUs.

As discussed above, video decoder 30 may also include inter-layerprediction unit 166. Inter-layer prediction unit 166 is configured topredict a current block (e.g., a current block in the EL) using one ormore different layers that are available in SVC (e.g., a base orreference layer). Such prediction may be referred to as inter-layerprediction. Inter-layer prediction unit 166 utilizes prediction methodsto reduce inter-layer redundancy, thereby improving coding efficiencyand reducing computational resource requirements. Some examples ofinter-layer prediction include inter-layer intra prediction, inter-layermotion prediction, and inter-layer residual prediction. Inter-layerintra prediction uses the reconstruction of co-located blocks in thebase layer to predict the current block in the enhancement layer.Inter-layer motion prediction uses motion information of the base layerto predict motion in the enhancement layer. Inter-layer residualprediction uses the residue of the base layer to predict the residue ofthe enhancement layer. Each of the inter-layer prediction schemes isdiscussed below in greater detail.

Reconstruction unit 158 may use the residual video blocks associatedwith TUs of a CU and the predicted video blocks of the PUs of the CU,e.g., either intra-prediction data or inter-prediction data, asapplicable, to reconstruct the video block of the CU. Thus, videodecoder 30 may generate a predicted video block and a residual videoblock based on syntax elements in the bitstream and may generate a videoblock based on the predicted video block and the residual video block.

After reconstruction unit 158 reconstructs the video block of the CU,filter unit 159 may perform a deblocking operation to reduce blockingartifacts associated with the CU. After filter unit 159 performs adeblocking operation to reduce blocking artifacts associated with theCU, video decoder 30 may store the video block of the CU in decodedpicture buffer 160. Decoded picture buffer 160 may provide referencepictures for subsequent motion compensation, intra prediction, andpresentation on a display device, such as display device 32 of FIG. 1Aor 1B. For instance, video decoder 30 may perform, based on the videoblocks in decoded picture buffer 160, intra prediction or interprediction operations on PUs of other CUs.

Multi-Layer Decoder

FIG. 3B is a block diagram illustrating an example of a multi-layervideo decoder 33 that may implement techniques in accordance withaspects described in this disclosure. The video decoder 33 may beconfigured to process multi-layer video frames, such as for SHVC andmultiview coding. Further, the video decoder 33 may be configured toperform any or all of the techniques of this disclosure.

The video decoder 33 includes a video decoder 30A and video decoder 30B,each of which may be configured as the video decoder 30 and may performthe functions described above with respect to the video decoder 30.Further, as indicated by the reuse of reference numbers, the videodecoders 30A and 30B may include at least some of the systems andsubsystems as the video decoder 30. Although the video decoder 33 isillustrated as including two video decoders 30A and 30B, the videodecoder 33 is not limited as such and may include any number of videodecoder 30 layers. In some embodiments, the video decoder 33 may includea video decoder 30 for each picture or frame in an access unit. Forexample, an access unit that includes five pictures may be processed ordecoded by a video decoder that includes five decoder layers. In someembodiments, the video decoder 33 may include more decoder layers thanframes in an access unit. In some such cases, some of the video decoderlayers may be inactive when processing some access units.

In addition to the video decoders 30A and 30B, the video decoder 33 mayinclude an upsampling unit 92. In some embodiments, the upsampling unit92 may upsample a base layer of a received video frame to create anenhanced layer to be added to the reference picture list for the frameor access unit. This enhanced layer can be stored in the decoded picturebuffer 160. In some embodiments, the upsampling unit 92 can include someor all of the embodiments described with respect to the resampling unit90 of FIG. 2A. In some embodiments, the upsampling unit 92 is configuredto upsample a layer and reorganize, redefine, modify, or adjust one ormore slices to comply with a set of slice boundary rules and/or rasterscan rules. In some cases, the upsampling unit 92 may be a resamplingunit configured to upsample and/or downsample a layer of a receivedvideo frame

The upsampling unit 92 may be configured to receive a picture or frame(or picture information associated with the picture) from the decodedpicture buffer 160 of the lower layer decoder (e.g., the video decoder30A) and to upsample the picture (or the received picture information).This upsampled picture may then be provided to the prediction processingunit 152 of a higher layer decoder (e.g., the video decoder 30B)configured to decode a picture in the same access unit as the lowerlayer decoder. In some cases, the higher layer decoder is one layerremoved from the lower layer decoder. In other cases, there may be oneor more higher layer decoders between the layer 0 decoder and the layer1 decoder of FIG. 3B.

In some cases, the upsampling unit 92 may be omitted or bypassed. Insuch cases, the picture from the decoded picture buffer 160 of the videodecoder 30A may be provided directly, or at least without being providedto the upsampling unit 92, to the prediction processing unit 152 of thevideo decoder 30B. For example, if video data provided to the videodecoder 30B and the reference picture from the decoded picture buffer160 of the video decoder 30A are of the same size or resolution, thereference picture may be provided to the video decoder 30B withoutupsampling. Further, in some embodiments, the upsampling unit 92 may bea resampling unit 90 configured to upsample or downsample a referencepicture received from the decoded picture buffer 160 of the videodecoder 30A.

As illustrated in FIG. 3B, the video decoder 33 may further include ademultiplexor 99, or demux. The demux 99 can split an encoded videobitstream into multiple bitstreams with each bitstream output by thedemux 99 being provided to a different video decoder 30A and 30B. Themultiple bitstreams may be created by receiving a bitstream and each ofthe video decoders 30A and 30B receives a portion of the bitstream at agiven time. While in some cases the bits from the bitstream received atthe demux 99 may be alternated one bit at a time between each of thevideo decoders (e.g., video decoders 30A and 30B in the example of FIG.3B), in many cases the bitstream is divided differently. For example,the bitstream may be divided by alternating which video decoder receivesthe bitstream one block at a time. In another example, the bitstream maybe divided by a non-1:1 ratio of blocks to each of the video decoders30A and 30B. For instance, two blocks may be provided to the videodecoder 30B for each block provided to the video decoder 30A. In someembodiments, the division of the bitstream by the demux 99 may bepreprogrammed. In other embodiments, the demux 99 may divide thebitstream based on a control signal received from a system external tothe video decoder 33, such as from a processor on a destination deviceincluding the destination module 14. The control signal may be generatedbased on the resolution or bitrate of a video from the input interface28, based on a bandwidth of the link 16, based on a subscriptionassociated with a user (e.g., a paid subscription versus a freesubscription), or based on any other factor for determining a resolutionobtainable by the video decoder 33.

Intra Random Access Point (IRAP) Pictures

Some video coding schemes may provide various random access pointsthroughout the bitstream such that the bitstream may be decoded startingfrom any of those random access points without needing to decode anypictures that precede those random access points in the bitstream. Insuch video coding schemes, all pictures that follow a random accesspoint in output order (e.g., including those pictures that are in thesame access unit as the picture providing the random access point) canbe correctly decoded without using any pictures that precede the randomaccess point. For example, even if a portion of the bitstream is lostduring transmission or during decoding, a decoder can resume decodingthe bitstream starting from the next random access point. Support forrandom access may facilitate, for example, dynamic streaming services,seek operations, channel switching, etc.

In some coding schemes, such random access points may be provided bypictures that are referred to as intra random access point (TRAP)pictures. For example, a random access point (e.g., provided by anenhancement layer IRAP picture) in an enhancement layer (“layerA”)contained in an access unit (“auA”) may provide layer-specific randomaccess such that for each reference layer (“layerB”) of layerA (e.g., areference layer being a layer that is used to predict layerA) having arandom access point contained in an access unit (“auB”) that is inlayerB and precedes auA in decoding order (or a random access pointcontained in auA), the pictures in layerA that follow auB in outputorder (including those pictures located in auB), are correctly decodablewithout needing to decode any pictures in layerA that precede auB.

IRAP pictures may be coded using intra prediction (e.g., coded withoutreferring to other pictures), and may include, for example,instantaneous decoder refresh (IDR) pictures, clean random access (CRA)pictures, and broken link access (BLA) pictures. When there is an IDRpicture in the bitstream, all the pictures that precede the IDR picturein decoding order are not used for prediction by pictures that followthe IDR picture in decoding order. When there is a CRA picture in thebitstream, the pictures that follow the CRA picture may or may not usepictures that precede the CRA picture in decoding order for prediction.Those pictures that follow the CRA picture in decoding order but usepictures that precede the CRA picture in decoding order may be referredto as random access skipped leading (RASL) pictures. Another type ofpicture that follows an TRAP picture in decoding order and precedes theTRAP picture in output order is a random access decodable leading (RADL)picture, which may not contain references to any pictures that precedethe TRAP picture in decoding order. RASL pictures may be discarded bythe decoder if the pictures that precede the CRA picture are notavailable. A BLA picture indicates to the decoder that pictures thatprecede the BLA picture may not be available to the decoder (e.g.,because two bitstreams are spliced together and the BLA picture is thefirst picture of the second bitstream in decoding order). An access unit(e.g., a group of pictures consisting of all the coded picturesassociated with the same output time across multiple layers) containinga base layer picture (e.g., a picture having a layer ID value of 0) thatis an TRAP picture may be referred to as an TRAP access unit.

Cross-Layer Alignment of IRAP Pictures

In SVC, TRAP pictures may not be required to be aligned (e.g., containedin the same access unit) across different layers. For example, if TRAPpictures were required to be aligned, any access unit containing atleast one TRAP picture would only contain TRAP pictures. On the otherhand, if TRAP pictures were not required to be aligned, in a singleaccess unit, one picture (e.g., in a first layer) may be an TRAPpicture, and another picture (e.g., in a second layer) may be a non-TRAPpicture. Having such non-aligned TRAP pictures in a bitstream mayprovide some advantages. For example, in a two-layer bitstream, if thereare more TRAP pictures in the base layer than in the enhancement layer,in broadcast and multicast applications, low tune-in delay and highcoding efficiency can be achieved.

In some video coding schemes, a picture order count (POC) may be used tokeep track of the relative order in which the decoded pictures aredisplayed. Some of such coding schemes may cause the POC values to bereset (e.g., set to zero or set to some value signaled in the bitstream)whenever certain types of pictures appear in the bitstream. For example,the POC values of certain IRAP pictures may be reset, causing the POCvalues of other pictures preceding those TRAP pictures in decoding orderto also be reset. This may be problematic when the TRAP pictures are notrequired to be aligned across different layers. For example, when onepicture (“picA”) is an TRAP picture and another picture (“picB”) in thesame access unit is not an TRAP picture, the POC value of a picture(“picC”), which is reset due to picA being an TRAP picture, in the layercontaining picA may be different from the POC value of a picture(“picD”), which is not reset, in the layer containing picB, where picCand picD are in the same access unit. This causes picC and picD to havedifferent POC values even though they belong to the same access unit(e.g., same output time). Thus, in this example, the derivation processfor deriving the POC values of picC and picD can be modified to producePOC values that are consistent with the definition of POC values andaccess units.

Picture Order Count (POC)

As discussed above, the value of a picture order count (POC) (e.g.,PicOrderCntVal in HEVC) for a particular coded picture denotes therelative order of the particular coded picture in the picture outputprocess with respect to other pictures in the same coded video sequence.In some embodiments, the POC comprises least significant bits (LSB) andmost significant bits (MSB), and the POC may be obtained byconcatenating the MSB and the LSB. In other embodiments, the POC may beobtained by adding the MSB value and the LSB value. The LSB may besignaled in the slice header, and the MSB may be computed by the encoderor the decoder based on the NAL unit type of the current picture and theMSB and LSB of one or more previous pictures in decoding order that are(1) not RASL or RADL pictures, (2) not discardable (e.g., picturesmarked as “discardable,” indicating that no other picture depends onthem, thereby allowing them to be dropped to satisfy bandwidthconstraints), (3) not sub-layer non-reference pictures (e.g., picturesthat are not used for reference by other pictures in the same temporalsub-layer or the same layer), (4) has a temporal ID (e.g., temporalsub-layer ID) equal to 0. Such pictures described in (1)-(4) may bereferred to herein as POC-anchor pictures. Similarly, pictures having atemporal ID value greater than 0, RASL or RADL pictures, discardablepictures, or sub-layer non-reference pictures may be referred to asnon-POC-anchor pictures. POC-anchor pictures may further includepictures that an encoder and/or a decoder may not elect to remove fromthe bitstream (e.g., to satisfy a bandwidth constraint). POC-anchorpictures may further include any picture other than the types ofpictures that an encoder and/or a decoder may be configured to removefrom the bitstream (e.g., to satisfy a bandwidth constraint).Non-POC-anchor pictures may include any picture that is not a POC-anchorpicture.

When the current picture is (1) an TRAP picture with NoRaslOutputFlag(e.g., a flag that indicates that RASL pictures are not to be output ifset to 1 and indicates that RASL pictures are to be output if set to 0)equal to 1, or (2) a CRA picture that is the first picture of thebitstream, the value of POC MSB is inferred to be equal to 0. Asdescribed above, in a multi-layer bitstream (e.g., SHVC or MV-HEVCbitstream with more than one layer), there may exist access units (AU)where one or more pictures are TRAP pictures and one or more otherpictures are non-TRAP pictures, and such AUs may be referred to as“non-aligned TRAP AUs.” When decoding bitstreams containing non-alignedTRAP AUs, it is possible (and likely) that the POCs derived based on thePOC LSB values signaled in the bitstream would violate the bitstreamconformance requirement that all pictures in an access unit should havethe same POC value.

In some embodiments, a POC reset flag (e.g., poc_reset_flag) may be usedto reset the POC of the pictures such that even when non-aligned TRAPAUs are present in the bitstream, the POC value of the current pictureand the pictures in the DPB are adjusted such that the POC of all thepictures in an AU are the same.

In some embodiments, instead of a single POC reset flag, two flags maybe used: a POC MSB reset flag (e.g., poc_msb_reset_flag) and a POC LSBreset flag (e.g., poc_lsb_reset_flag). The former (i.e., thepoc_msb_reset_flag) resets the MSB of the POC, and the latter (i.e., thepoc-lsb_reset_flag) resets the LSB of the POC. Both of these flags maybe signaled in the slice header.

For example, if a particular picture has a POC value of 233, and the MSBand the LSB of the POC constitute 1 bit and 7 bits, respectively, theMSB would be “1” (e.g., having a value of 128) and the LSB would be“1101001” (e.g., having a value of 105). Thus, if only the MSB of thePOC is reset (e.g., in response to processing poc_msb_reset_flag havinga value of 1), the POC value becomes 105, and if only the LSB are reset(e.g., in response to processing poc_lsb_reset_flag having a value of1), the POC value becomes 128. If both the MSB and the LSB are reset(e.g., in response to processing poc_msb_reset_flag andpoc_lsb_reset_flag, each having a value of 1), the POC value becomes 0.

Resetting of POC Values

With reference to FIGS. 4-7, the motivation for resetting the POC values(e.g., the LSB and the MSB) in non-aligned TRAP AUs will be described.As described above, in some coding schemes, certain conformanceconstraints may specify that the POC of all coded pictures in a singleAU should be the same. Without appropriate resets of the POC values,non-aligned TRAP AUs in the bitstream may produce POC values thatviolate such conformance constraints.

FIG. 4 shows a multi-layer bitstream 400 including an enhancement layer(EL) 410 and a base layer (BL) 420. The EL 410 includes EL pictures412-418, and the BL includes BL pictures 422-428. The multi-layerbitstream 400 further includes access units (AUs) 430-460. The AU 430includes the EL picture 412 and the BL picture 422, the AU 440 includesthe EL picture 414 and the BL picture 424, the AU 450 includes the ELpicture 416 and the BL picture 426, and the AU 460 includes the ELpicture 418 and the BL picture 428. In the example of FIG. 4, the ELpicture 414 is an IDR picture, and the corresponding BL picture 424 inthe AU 440 is a trailing picture (e.g., a non-TRAP picture), andconsequently, the AU 440 is a non-aligned TRAP AU. In some embodiments,an MSB reset is performed at a given picture if the picture is an IDRpicture that is not in the base layer. Such an IDR picture may have anon-zero POC LSB value.

FIG. 5 shows a table 500 that illustrates the POC values that may besignaled or derived in connection with the multi-layer bitstream 400 ofFIG. 4. As shown in FIG. 5, the MSB of the POC in the EL 410 is reset atthe EL picture 414, while the MSB of the POC in the BL 420 is not reset.Thus, if a reset is not performed in the BL 420 at the BL picture 424 inthe non-aligned TRAP AU 440, the POC values of BL pictures and the ELpictures in the AUs 440-460 would not match (i.e., be equivalent) asspecified by the conformance constraints. The differences in the POCvalues with and without a reset are highlighted in bold in FIG. 5.

FIG. 6 shows a multi-layer bitstream 600 including an enhancement layer(EL) 610 and a base layer (BL) 620. The EL 610 includes EL pictures612-618, and the BL includes BL pictures 622-628. The multi-layerbitstream 600 further includes access units (AUs) 630-660. The AU 630includes the EL picture 612 and the BL picture 622, the AU 640 includesthe EL picture 614 and the BL picture 624, the AU 650 includes the ELpicture 616 and the BL picture 626, and the AU 660 includes the ELpicture 618 and the BL picture 628. In the example of FIG. 6, the BLpicture 624 is an IDR picture, and the corresponding EL picture 614 inthe AU 640 is a trailing picture (e.g., a non-TRAP picture), andconsequently, the AU 640 is a non-aligned IRAP AU. In some embodiments,an MSB reset and an LSB reset are performed for a given picture if thepicture is an IDR picture that is in the base layer. For example, thebitstream may include an indication that the POC MSB and the POC LSB ofsuch a BL IDR picture should be reset. Alternatively, the decoder mayperform the reset of the POC MSB and the POC LSB of such a BL IDRpicture without any indication in the bitstream that a POC reset shouldbe performed.

FIG. 7 shows a table 700 that illustrates the POC values that may besignaled or derived in connection with the multi-layer bitstream 600 ofFIG. 6. As shown in FIG. 7, the MSB and the LSB of the POC in the BL 620is reset at the BL picture 624, while neither the MSB nor the LSB of thePOC in the EL 610 is reset. Thus, if a reset of the MSB and the LSB ofthe POC is not performed in the EL 610 at the EL picture 614 in thenon-aligned TRAP AU 640, the POC values of BL pictures and the ELpictures in the AUs 640-660 would not match as specified by theconformance constraints. The differences in the POC values with andwithout a reset are highlighted in bold in FIG. 7.

The embodiments described herein are not limited to the examplebitstream configurations illustrated in FIGS. 4 and 6, and thetechniques described herein may be extended to any multi-layer bitstreamhaving any number of layers, access units, and pictures. Also, in theexamples illustrated in FIGS. 4-7, the LSB of the POC is representedusing seven bits. However, the techniques described herein may beextended to scenarios having any forms of POC value representation.

Reset of Preceding Pictures and Loss of Reset Pictures

When an MSB reset or an LSB reset is performed at a particular picture,other pictures in the same layer that precede the particular picture indecoding order are also reset based on the reset performed at theparticular picture. For example, in the example of FIG. 6, the ELpicture 614 has a POC value of 241 (e.g., LSB of “1110001”+MSB of “1”,which is 113+128). When the MSB and LSB resets are performed at the ELpicture 614, the POC value of the EL picture 614 becomes 0, and the ELpicture 612 in the EL 610 which precedes the EL picture 614 in decodingorder is also reset based on the original POC value of 241 of the ELpicture 614. For example, the new POC value of the EL picture 612 iscalculated by subtracting the pre-reset POC value of the EL picture 614(which is a value of 241) from the pre-reset POC value of the EL picture612, which is 240 (e.g., LSB of “1110000”+MSB of “1”, which is 112+128).Thus, after the reset, the POC value of the EL picture 612 becomes −1,in accordance with the fact that the EL picture 612 is to be outputbefore the EL picture 614, where a smaller POC value denotes an earlierposition in output order. As shown in FIG. 7, the signaled LSB valuesfor the subsequent AUs 650 and 660 are adjusted accordingly (e.g., to 1and 2, respectively), with the assumption that the reset is performed atthe EL picture 614.

However, even if an appropriate POC reset of the MSB and/or the LSBdescribed above is signaled in the bitstream (e.g., in the slice header)so that the decoder can process the signal and perform the POC resetaccordingly, if the picture signaling such a POC reset is lost duringtransmission of the bitstream or removed from the bitstream in order tosatisfy bandwidth constraints, the POC reset intended to be performed atthe particular picture may not be properly performed.

For example, in the example of FIG. 6, if the EL picture 614 isunavailable to the decoder, the decoder would not know (i.e., would notdetermine) to reset the MSB and LSB of the POC in the EL 610 at the AU640. Consequently, the POC values of the any pictures preceding theunavailable EL picture 614 in decoding order would still have theiroriginal, pre-reset POC values since the reset at the EL picture 614never took place (i.e., the reset operation was not performed). On theother hand, the POC values of the pictures following the unavailable ELpicture 614 in decoding order would have been determined or signaled asif reset actually took place (i.e., the reset operation was performed).Thus, in the example of FIG. 7, the EL pictures 612, 616, and 618 wouldhave POC values of 240, 1, and 2, respectively, which would be incorrectgiven that the EL picture 612 precedes the EL pictures 616 and 618 inoutput order. Thus, a coding method that results in correct POC values,even when the picture signaling the POC reset becomes unavailable, isdesired.

Examples and Implementations

Several methods that may be used to address certain problems describedabove will be described below. Some of these methods may be appliedindependently, and some of them may be applied in combination. Inaddition, the example syntax and semantics that may be used to implementone or more of the methods described herein are also provided below.When certain portions of the HEVC specification are reproduced toillustrate the additions and deletions that may be incorporated toimplement one or more of the methods described herein, suchmodifications are shown in italics and strikethrough, respectively.

Signaling Values for POC Derivation

In some embodiments, an SEI message that contains information forcorrect POC derivation is signaled for one or more pictures that followthe picture for which the POC MSB and/or the POC LSB is to be reset. Forexample, the SEI message may be associated with a picture, picA, thatfollows another picture, picB, for which the POC MSB, the POC LSB, orboth are to be reset. Thus, even when picB is entirely lost, the SEImessage associated with picA can be used to derive the correct POCvalues for other pictures in the same layer.

In some embodiments, the information for correct POC derivation issignaled in the slice header of one or more pictures that follow thepicture for which the POC MSB and/or the POC LSB is to be reset. Forexample, the information may be included in the slice header of apicture picA that follows another picture picB for which the POC MSB,the POC LSB, or both are to be reset. Thus, even when picB is entirelylost, the information included in the slice header of picA can be usedto derive the correct POC values for other pictures in the same layer.

Derivation of Correct POC Based on Signaled Values

FIG. 8 is a flowchart illustrating a method 800 for coding videoinformation, according to an embodiment of the present disclosure. Thesteps illustrated in FIG. 8 may be performed by an encoder (e.g., thevideo encoder as shown in FIG. 2A or FIG. 2B), a decoder (e.g., thevideo decoder as shown in FIG. 3A or FIG. 3B), or any other component.For convenience, method 800 is described as performed by a coder, whichmay be the encoder, the decoder, or another component.

The method 800 begins at block 801. At block 805, the coder processesPOC derivation information associated with a picture. In someembodiments, the processing of the POC derivation information mayinclude signaling the POC derivation information in a bitstream. Asdescribed above, the POC derivation information may be signaled in theslice header of the picture and/or signaled as an SEI message associatedwith the picture. In some embodiments, the processing of the POCderivation information may include processing the POC derivationinformation included in a bitstream. For example, the POC derivationinformation may include: a POC reset type indicating whether the POCvalue of the preceding POC-reset picture (e.g., a picture at which a POCreset is to be performed) in the same layer is to be reset by resettingboth most significant bits (MSB) and least significant bits (LSB) of thePOC value or by resetting only the MSB of the POC value; a POC resetvalue indicating the POC value of the picture that was lost or removedthat also precedes the picture with which the POC derivation informationis associated; and a POC reset ID identifying the POC reset for whichthe POC derivation information is provided. For example, the decoder mayskip a POC reset signaled in connection with a particular picture if thesignaled POC reset has a POC reset ID value of 1 and another POC resethaving a POC reset ID of 1 has already been performed.

At block 810, the coder determines the POC of another picture thatprecedes the picture in decoding order. In the example shown in FIG. 7,even if the EL picture 614 containing the POC value reset instruction islost or otherwise removed, the POC value of the EL picture 612 would becorrectly reset using the POC derivation information, for example,associated with the EL pictures 616 and/or 618. The method 800 ends at815.

As discussed above, one or more components of video encoder 20 of FIG.2A, video encoder 23 of FIG. 2B, video decoder 30 of FIG. 3A, or videodecoder 33 of FIG. 3B (e.g., inter-layer prediction unit 128 and/orinter-layer prediction unit 166) may be used to implement any of thetechniques discussed in the present disclosure, such as processing thePOC derivation information associated with one or more pictures, anddetermining the POC of another picture that precedes the one or morepictures in decoding order.

Disabling POC Reset in Non-POC-Anchor Pictures

In some embodiments, a conformance constraint may be applied (e.g., aconformance constraint may be determined to be applicable and thenadhered to based on the performance of operation(s)), for example by acoder, to the bitstream such that the value of neitherpoc_lsb_reset_flag nor poc_msb_reset_flag is set equal to 1 when theslice segment belongs to a picture that is not a POC-anchor picture. Asdescribed above, such a picture may be a sub-layer non-referencepicture, a discardable picture, a RASL picture, a RADL picture, or apicture that has a temporal ID greater than 0. For example, thesub-layer non-reference picture may refer to a picture that is not usedfor reference by other pictures of the highest temporal layer. Thediscardable picture may refer to a picture that is not used forreference by any other picture. For example, such discardable picturesmay be marked “discardable.” Such discardable pictures may be removedfrom the bitstream by the encoder or the decoder in order to satisfybandwidth constraints. In some embodiments, a discardable pictureincludes any picture that may be removed from the bitstream by choice(e.g., by the decoder or some middlebox). The RASL and RADL picturesrefer to leading pictures, and RASL pictures may not be output if thedecoding process starts at the TRAP picture associated with the RASLpicture. The picture having a temporal ID greater than 0 may be apicture that may be removed from the bitstream if the frame rate isswitched down to a sufficiently low value. For example, if a bitstreamcontains three temporal sub-layers, the pictures from all three temporalsub-layers may be displayed in order to operate at 90 frames per second(fps), the pictures from the lower two temporal sub-layers may bedisplayed in order to operate at 60 fps, and the pictures from thelowest temporal sub-layer may be displayed in order to operate at 30fps. As discussed above, bitstream constraints or other performanceconstraints may cause one or more pictures to be removed or dropped fromthe bitstream (e.g., a coder may evaluate such constraints and, based onthis evaluation, perform operations in accordance with the constraintssuch that one or more pictures are caused to be removed from thebitstream or dropped from the bitstream), and in this example, thepictures from the highest temporal sub-layer may be removed beforeremoving pictures from the next highest temporal sub-layer, and so on.For example, the pictures in the lowest temporal sub-layer may not beremoved from the bitstream until the pictures in all the other temporalsub-layers are removed. Thus, pictures having a temporal ID greater than0 (where a temporal ID of 0 corresponds to the lowest temporalsub-layer) are more likely to be removed from the bitstream.

As described herein, these pictures (e.g., a sub-layer non-referencepicture, a discardable picture, a RASL picture, a RADL picture, apicture that has a temporal ID greater than 0, and the like) may bereferred to as non-POC-anchor pictures. In some embodiments, becausethese pictures are more likely to be removed from the bitstream (e.g.,to satisfy certain bandwidth constraints), a constraint that specifiesthat these pictures cannot trigger a POC reset may be introduced toreduce the likelihood that a POC-reset picture may be removed from thebitstream. For example, if a discardable picture is not allowed totrigger a POC reset (e.g., by signaling a POC MSB reset, a POC LSBreset, or both), even if the discardable picture is discarded, theunavailability of that discardable picture to the decoder would notresult in the problems described above regarding POC resets.

In some embodiments, the coder may determine that a POC reset should besignaled in connection with a particular picture, subsequently determinethat the particular picture is a sub-layer non-reference picture, adiscardable picture, a RASL picture, a RADL picture, a picture that hasa temporal ID greater than 0, or a picture that is otherwise likely tobe removed from the bitstream, and thus refrain from signaling a POCreset in the particular picture or signal that a POC reset is not to beperformed at the particular picture. In some embodiments, the coder maydetermine that a POC reset should be signaled in connection with aparticular picture, and subsequently prevent the particular picture frombeing a non-POC-anchor picture (e.g., by preventing the particularpicture from having certain picture types). In some embodiments, thedetermination of whether a POC reset should be performed at theparticular picture may be based at least in part on whether theparticular picture is a sub-layer non-reference picture, a discardablepicture, a RASL picture, a RADL picture, a picture that has a temporalID greater than 0, or a picture that is otherwise likely to be removedfrom the bitstream. In such embodiments, if the particular picture isnot a POC-anchor picture, the coder indicates in the bitstream that thePOC reset is not to be performed at the particular picture.Alternatively, the coder may simply not provide any indication in thebitstream that a POC reset is to be performed at the particular picture.Similarly, if the particular picture is a POC-anchor picture, the coder,if a POC reset is determined to be needed at the particular picture,indicate in the bitstream that the POC reset is to be performed at theparticular picture. Alternatively, the coder may simply not provide anyindication in the bitstream that the POC reset is not to be performed orthat the POC reset should not be performed at the particular picture.

Disabling of POC Reset in Non-POC-Anchor Pictures

FIG. 9 is a flowchart illustrating a method 900 for coding videoinformation, according to an embodiment of the present disclosure. Thesteps illustrated in FIG. 9 may be performed by an encoder (e.g., thevideo encoder as shown in FIG. 2A or FIG. 2B), a decoder (e.g., thevideo decoder as shown in FIG. 3A or FIG. 3B), or any other component.For convenience, method 900 is described as performed by a coder, whichmay be the encoder, the decoder, or another component.

The method 900 begins at block 901. At block 905, the coder determineswhether a picture is a POC-anchor picture. For example, POC-anchorpictures may include any pictures that are: (1) not RASL or RADLpictures, (2) not discardable (e.g., pictures marked as “discardable,”indicating that no other picture depends on them, thereby allowing themto be dropped to satisfy bandwidth constraints), (3) not sub-layernon-reference pictures (e.g., pictures that are not used for referenceby other pictures in higher temporal layers), (4) has a temporal ID(e.g., temporal sub-layer ID) equal to 0, and/or (5) any other picturethat is otherwise likely to be removed from the bitstream. If the coderdetermines that the picture is not a POC-anchor picture, the method 900proceeds to 910. On the other hand, if the coder determines that thepicture is a POC-anchor picture, the method 900 proceeds to 915.

At block 910, the coder signals for the picture that the POC reset isnot to be performed at the picture. For example, the coder may signalone or more flags that indicate that neither the POC LSB reset nor thePOC MSB reset is to be performed in connection with the picture. In someembodiments, the coder may not signal or otherwise provide anyindication in the bitstream that a POC reset is to be performed at thepicture. For example, during the decoding process, if no signal orindication that indicates that a POC reset is to be performed isprovided in the bitstream, the decoder may not perform a POC reset atthat picture.

At block 915, the coder signals a POC reset for the picture. Forexample, the coder may signal one or more flags in the bitstream thatindicate that a POC LSB reset, a POC MSB reset, or both are to beperformed. In some embodiments, the coder may not signal or otherwiseprovide any indication in the bitstream that a POC reset is not to beperformed at the picture. For example, during the decoding process, thedecoder may infer or determine from other signals or indications in thebitstream that a POC reset is to be performed, and that if no additionalsignal or indication disabling the POC reset is provided in thebitstream, the decoder should perform the POC reset as inferred ordetermined. The method 900 ends at 920.

As discussed above, one or more components of video encoder 20 of FIG.2A, video encoder 23 of FIG. 2B, video decoder 30 of FIG. 3A, or videodecoder 33 of FIG. 3B (e.g., inter-layer prediction unit 128 and/orinter-layer prediction unit 166) may be used to implement any of thetechniques discussed in the present disclosure, such as determiningwhether a picture is a POC-anchor picture, enabling a POC reset,disabling a POC reset, providing an indication in the bitstream that aPOC reset is to be performed, and providing an indication in thebitstream that a POC reset is not to be performed.

In the method 900, one or more of the blocks shown in FIG. 9 may beremoved (e.g., not performed) and/or the order in which the method isperformed may be switched. For example, although block 910 is shown inFIG. 9, block 910 may be removed, and the method 900 may end withoutperforming any additional operations if the coder determines that thepicture is not a POC-anchor picture. Alternatively, block 915 may beremoved, and the method 900 may end without performing any additionaloperations if the coder determines that the picture is a POC-anchorpicture. Thus, the embodiments of the present disclosure are not limitedto or by the example shown in FIG. 9, and other variations may beimplemented without departing from the spirit of this disclosure.

IRAP Pictures in Non-Aligned IRAP AU

In some embodiments, a conformance constraint may be applied to thebitstream such that when an access unit contains at least one picturethat is an TRAP picture with NoRaslOutputFlag equal to 1, a POC MSB(e.g., MSB of the POC) reset shall be performed for all pictures in theaccess unit that are not TRAP pictures. In such embodiments,poc_msb_reset_flag associated with the non-TRAP pictures may be set to 1(e.g., indicating that a POC MSB reset is to be performed at suchnon-TRAP pictures). For example, if Picture A is an TRAP picture in anaccess unit that immediately follows a splice point (e.g., indicated byNoRaslOutputFlag value of 1), and Picture B that is in the same accessunit as Picture A is a non-TRAP picture, a POC MSB reset may be signaledin the bitstream for Picture B.

FIG. 10 is a flowchart illustrating a method 1000 for coding videoinformation, according to an embodiment of the present disclosure. Thesteps illustrated in FIG. 10 may be performed by an encoder (e.g., thevideo encoder as shown in FIG. 2A or FIG. 2B), a decoder (e.g., thevideo decoder as shown in FIG. 3A or FIG. 3B), or any other component.For convenience, method 1000 is described as performed by a coder, whichmay be the encoder, the decoder, or another component.

The method 1000 begins at block 1001. At block 1005, the coderdetermines whether a picture is an TRAP picture. As described above, insome embodiments, an TRAP picture may be an IDR picture, a CRA picture,or a BLA picture. In some embodiments, the coder may further determine,based on information included in the bitstream, whether the picture isin an access unit that immediately follows a splice point. In someembodiments, the coder may further determine, instead of determiningwhether the picture is in an access unit that immediately follows asplice point, whether pictures preceding the picture in decoding ordershould be output. For example, whether the picture is in an access unitthat immediately follows a splice point or whether pictures precedingthe picture in decoding order should be output may be indicated by oneor more variables that are signaled or indicated in the bitstream orderived from other information available to the coder (e.g.,NoRaslOutputFlag). For example, for IDR pictures and CRA pictures,NoRaslOutputFlag may be derived from other information included in thebitstream. For BLA pictures, the presence of such BLA pictures mayindicate to the decoder that the BLA pictures immediately follow asplice point. If the coder determines that the picture is an TRAPpicture, the method 1000 proceeds to block 1010. Otherwise, the method1000 ends at 1015.

At block 1010, the coder enables a POC MSB reset for all other non-TRAPpictures in the access unit. In some embodiments, the coder enables aPOC MSB reset for all other non-TRAP pictures in the access unit thatimmediately follow a splice point in decoding order. For example, thecoder may signal a POC MSB reset flag (e.g., poc_msb_reset_flag) havinga value of 1, indicating that a POC MSB reset is to be performed foreach of the non-TRAP pictures. The method 1000 ends at 1015.

As discussed above, one or more components of video encoder 20 of FIG.2A, video encoder 23 of FIG. 2B, video decoder 30 of FIG. 3A, or videodecoder 33 of FIG. 3B (e.g., inter-layer prediction unit 128 and/orinter-layer prediction unit 166) may be used to implement any of thetechniques discussed in the present disclosure, such as determiningwhether a picture is an TRAP picture, and enabling a POC MSB reset forall other non-TRAP pictures in the access unit.

In the method 1000, one or more of the blocks shown in FIG. 10 may beremoved (e.g., not performed) and/or the order in which the method isperformed may be switched. Thus, the embodiments of the presentdisclosure are not limited to or by the example shown in FIG. 10, andother variations may be implemented without departing from the spirit ofthis disclosure.

Base Layer IDR Pictures in Non-Aligned IRAP AU

In some embodiments, a conformance constraint may be applied to thebitstream such that when an access unit A contains a base layer picturethat is an IDR picture, a POC LSB (e.g., LSB of the POC) reset shall beperformed for all enhancement layer pictures in the access unit A thatare not IDR pictures or that have a non-zero POC LSB value signaled inthe bitstream. In such embodiments, the poc_lsb_reset_flag associatedwith the EL pictures (e.g., indicating that a POC LSB reset is to beperformed at such EL pictures). For example, if Picture A in the baselayer is an IDR picture, and Picture B that is in the same access unitas Picture A is not an IDR picture, a POC LSB reset may be signaled inthe bitstream for Picture B. In another example, if Picture A in thebase layer is an IDR picture, and Picture C in the same access unit asPicture A has a POC LSB value of 0 signaled in the bitstream, a POC LSBreset may not need to be signaled in the bitstream for Picture C.

FIG. 11 is a flowchart illustrating a method 1100 for coding videoinformation, according to an embodiment of the present disclosure. Thesteps illustrated in FIG. 11 may be performed by an encoder (e.g., thevideo encoder as shown in FIG. 2A or FIG. 2B), a decoder (e.g., thevideo decoder as shown in FIG. 3A or FIG. 3B), or any other component.For convenience, method 1100 is described as performed by a coder, whichmay be the encoder, the decoder, or another component.

The method 1100 begins at block 1101. At block 1105, the coderdetermines whether a picture is a base layer IDR picture. In someembodiments, the POC of a BL IDR picture is automatically reset to 0. Ifthe coder determines that the picture is a BL IDR picture, the method1100 proceeds to block 1110. Otherwise, the method 1100 ends at 1115.

At block 1110, the coder enables a POC LSB reset for all other non-IDRpictures in the access unit. For example, the coder may signal a POC LSBreset flag (e.g., poc_lsb_reset_flag) having a value of 1, indicatingthat a POC LSB reset is to be performed for each of the non-IDR picturesin the same access unit as the BL IDR picture. The method 1100 ends at1115.

As discussed above, one or more components of video encoder 20 of FIG.2A, video encoder 23 of FIG. 2B, video decoder 30 of FIG. 3A, or videodecoder 33 of FIG. 3B (e.g., inter-layer prediction unit 128 and/orinter-layer prediction unit 166) may be used to implement any of thetechniques discussed in the present disclosure, such as determiningwhether a picture is a BL IDR picture, and enabling a POC LSB reset forall other non-IDR pictures in the access unit.

In the method 1100, one or more of the blocks shown in FIG. 11 may beremoved (e.g., not performed) and/or the order in which the method isperformed may be switched. Thus, the embodiments of the presentdisclosure are not limited to or by the example shown in FIG. 11, andother variations may be implemented without departing from the spirit ofthis disclosure.

Signaling Backup Reset in Subsequent Pictures

In some embodiments, for each picture picA that resets its POC MSB valuein order to align the derived POC (e.g., PicOrderCntVal) with anotherpicture that is an IRAP picture with NoRaslOutputFlag equal to 1 andthat is in the same access unit as picA, an indication may be providedin the bitstream in association with one or more pictures in the samelayer as picA that follow picA in decoding order that a POC MSB reset isto be performed with the one or more pictures. For example,poc_msb_reset_flag having a value of 1 may be signaled for each of theone or more pictures.

FIG. 12 is a flowchart illustrating a method 1200 for coding videoinformation, according to an embodiment of the present disclosure. Thesteps illustrated in FIG. 12 may be performed by an encoder (e.g., thevideo encoder as shown in FIG. 2A or FIG. 2B), a decoder (e.g., thevideo decoder as shown in FIG. 3A or FIG. 3B), or any other component.For convenience, method 1200 is described as performed by a coder, whichmay be the encoder, the decoder, or another component.

The method 1200 begins at block 1201. At block 1205, the coderdetermines whether a POC MSB reset is to be performed at a particularpicture. As described above, in some embodiments, a POC MSB reset may beperformed in order to prevent pictures in different layers from havinginconsistent POC values in a non-aligned TRAP access unit. In someembodiments, the coder further determines whether the particular pictureis a non-TRAP picture in a non-aligned TRAP access unit. If the coderdetermines that a POC MSB reset is to be performed at the particularpicture, the method 1200 proceeds to block 1210. Otherwise, the method1200 ends at 1215.

At block 1210, the coder enables a POC MSB reset for one or morepictures that follow the particular picture in decoding order. In someembodiments, the one or more pictures may be in the same layer as theparticular picture. For example, the coder may signal a POC MSB resetflag (e.g., poc_msb_reset_flag) having a value of 1 for the picture thatimmediately follows the particular picture in decoding order, indicatingthat a POC MSB reset is to be performed for the picture that immediatelyfollows the particular picture in decoding order. As described above, ifthe particular picture having an indication that a POC MSB reset is tobe performed is lost, a back-up reset of the POC MSB at the picture thatimmediately follows the particular picture in decoding order based onthe indication associated with the picture that immediately follows theparticular picture in decoding order. In some embodiments, the coder mayfurther provide an indication or variable that may be used so that thePOC MSB reset is not performed more than once. Such an indication orvariable (e.g., a POC reset ID) may help in determining whether the POCMSB reset has been performed. In some embodiments, the coder enables thePOC MSB reset for the one or more pictures only if the particularpicture is a non-TRAP picture in a non-aligned TRAP access unit. Themethod 1200 ends at 1215.

As discussed above, one or more components of video encoder 20 of FIG.2A, video encoder 23 of FIG. 2B, video decoder 30 of FIG. 3A, or videodecoder 33 of FIG. 3B (e.g., inter-layer prediction unit 128 and/orinter-layer prediction unit 166) may be used to implement any of thetechniques discussed in the present disclosure, such as determiningwhether a POC MSB reset is to be performed at a particular picture, andenabling a POC MSB reset for one or more pictures that follow theparticular picture in decoding order.

In the method 1200, one or more of the blocks shown in FIG. 12 may beremoved (e.g., not performed) and/or the order in which the method isperformed may be switched. Thus, the embodiments of the presentdisclosure are not limited to or by the example shown in FIG. 12, andother variations may be implemented without departing from the spirit ofthis disclosure.

Signaling POC Values of Preceding Pictures

In some embodiments, for picture picA that resets its POC value in orderto align the derived PicOrderCntVal with an IDR picture that hasnuh_layer_id equal to 0 and that is in the same access unit as picA, thevalue of PicOrderCntVal of picA before POC reset is signaled for one ormore pictures that follow picA in decoding order and that have the samenuh_layer_id as picA.

Example Implementation Slice Segment Header Syntax

The following example slice segment header syntax may be used toimplement one or more of the embodiments described herein.

TABLE 1 Example Slice Segment Header Syntax Descriptorslice_segment_header( ) {  first_slice_segment_in_pic_flag u(1)  if(nal_unit_type >= BLA_W_LP && nal_unit_type <=   RSV_IRAP_VCL23 )  no_output_of_prior_pics_flag u(1)  slice_pic_parameter_set_id ue(v) if( !first_slice_segment_in_pic_flag ) {   if(dependent_slice_segments_enabled_flag )    dependent_slice_segment_flagu(1)   slice_segment_address u(v)  }  if( !dependent_slice_segment_flag) {   i = 0   if(num_extra_slice_header_bits > i) {    i++    poc_msb_reset_flag u(1)   }  if( num_extra_slice_header_bits > i) {    i++    poc_lsb_reset_flagu(1)   }   if( num_extra_slice_header_bits > i) {    i++   discardable_flag u(1)   }   for(  

 ; i < num_extra_slice_header_bits; i++ )    slice_reserved_flag[ i ]u(1)   slice_type ue(v)   if( output flag_present flag )   pic_output_flag u(1)   if( separate_colour_plane flag == 1 )   colour_plane_id u(2)   if( nuh_layer_id > 0 | |     ( nal_unit_type!= IDR_W_RADL &&      nal_unit_type !=       IDR_N_LP ) ) {   slice_pic_order_cnt_lsb u(v)   ...

Example Implementation Slice Segment Header Semantics

The following example semantics may be used to implement one or more ofthe embodiments described herein. Changes to the existing language inthe HEVC specification are shown in italics.

-   -   poc_msb_reset_flag equal to 1 specifies that the MSB value of        the derived picture order count for the current picture is equal        to 0. poc_msb_reset_flag equal to 0 specifies that the MSB value        of the derived picture order count for the current picture may        or may not be equal to 0.    -   When the current picture is not an IRAP picture with        NoRaslOutputFlag equal to 1 and at least one picture in the        current access unit is an IRAP picture with NoRaslOutputFlag        equal to 1, poc_msb_reset_flag shall be present and the value        shall be equal to 1.    -   When not present, the value of poc_msb_reset_flag is inferred to        be equal to 0.    -   poc_lsb_reset_flag equal to 1 specifies that the derived picture        order count for the current picture is equal to 0.        poc_lsb_reset_flag equal to 0 specifies that the derived picture        order count for the current picture may or may not be equal to        0.    -   When the current picture is not an IDR picture or        slice_pic_order_cnt_lsb is not equal to 0, and the picture with        nuh_layer_id equal to 0 in the current access unit is an IDR        picture, poc_lsb_reset_flag shall be present and the value shall        be equal to 1.    -   When not present, the value of poc_lsb_reset_flag is inferred to        be equal to 0.    -   When the value of poc_msb_reset_flag is equal to 0, the value of        poc_lsb_reset_flag shall be equal to 0.    -   It is a requirement of bitstream conformance that, when there is        an IRAP picture with NoRaslOutputFlag equal to 1 in the current        access unit, the current picture shall have discardable_flag        equal to 0 and TemporalId greater than 0, and shall not be a        sub-layer non-reference picture, a RASL picture, or a RADL        picture.

Alternatively, the following constraints could be added to the semanticsof the poc_msb_reset_flag and poc_lsb_reset_flag:

-   -   It is a requirement of bitstream conformance that for slices        that have value of nal_unit_type to be less than 16, and that        have nal_unit_type % 2=0, the value of both poc_lsb_reset_flag        and poc_msb_reset_flag shall be equal to 0.    -   It is a requirement of bitstream conformance that when the value        of either poc_lsb_reset_flag or poc_msb_reset_flag, or both, is        equal to 1, the value of discardable_flag, when present, shall        be equal to 0.

It is a requirement of bitstream conformance that when an access unitcontains a picture that is an IRAP picture with NoRaslOutputFlag equalto 1, then the following conditions apply: (1) if the picture withnuh_layer_id equal to 0 is an IDR picture, the value ofpoc_lsb_reset_flag and poc_msb_reset_flag shall be both set equal to 1for all pictures in that access unit that have nuh_layer_id not equal to0; and (2) otherwise, the value of poc_lsb_reset_flag shall be set equalto 1 and the value of poc_msb_reset_flag shall be both set equal to 1for all pictures in that access unit that are no TRAP picture withNoRaslOutputFlag equal to 1.

Example Implementation Decoding Process for POC and Reference PictureSet

An example derivation of the POC for each slice is described below. Whenthe value of poc_lsb_reset_flag or the poc_msb_reset_flag is set to 1,the POC of the current picture and all the pictures in the DPB that aremarked as “used for reference” or that are needed for output aredecremented.

Decoding Process for Picture Order Count

Output of this process is PicOrderCntVal, the picture order count of thecurrent picture.

Picture order counts are used to identify pictures, for deriving motionparameters in merge mode and motion vector prediction, and for decoderconformance checking.

Each coded picture is associated with a picture order count variable,denoted as PicOrderCntVal.

When the current picture is not an IRAP picture with NoRaslOutputFlagequal to 1, the variables prevPicOrderCntLsb and prevPicOrderCntMsb arederived as follows:

Let prevTid0Pic be the previous picture in decoding order that hasTemporalId equal to 0 and nuh_layer_id equal to nuh_layer_id of thecurrent picture and that is not a RASL picture, a RADL picture, or asub-layer non-reference picture, and let prevPicOrderCnt be equal toPicOrderCntVal of prevTid0Pic.

-   -   The variable prevPicOrderCntLsb is set equal to prevPicOrderCnt        & (        -   MaxPicOrderCntLsb−1).    -   The variable prevPicOrderCntMsb is set equal to prevPicOrderCnt−        -   prevPicOrderCntLsb.

The variable PicOrderCntMsb of the current picture is derived asfollows:

If the current picture is an IRAP picture with NoRaslOutputFlag equal to1, PicOrderCntMsb is set equal to 0.

Otherwise, PicOrderCntMsb is derived as follows:

-   -   if((slice_pic_order_cnt_lsb<prevPicOrderCntLsb) &&        -   ((prevPicOrderCntLsb−slice_pic_order_cnt_lsb)>=(    -   MaxPicOrderCntLsb/2)))        -   PicOrderCntMsb=prevPicOrderCntMsb+MaxPicOrderCntLsb    -   else if((slice_pic_order_cnt_lsb>prevPicOrderCntLsb) &&        -   ((slice_pic_order_cnt_lsb−prevPicOrderCntLsb)>(    -   MaxPicOrderCntLsb/2)))        -   PicOrderCntMsb=prevPicOrderCntMsb−MaxPicOrderCntLsb    -   else        -   PicOrderCntMsb=prevPicOrderCntMsb

PicOrderCntVal is derived as follows:

-   -   PicOrderCntVal=(poc_msb_reset_flag ? 0: PicOrderCntMsb)+        -   (poc_lsb_reset_flag ? 0: slice_pic_order_cnt_lsb)

It should be noted that all IDR pictures that have nuh_layer_id equal to0 will have PicOrderCntVal equal to 0 since slice_pic_order_cnt_lsb isinferred to be 0 for IDR pictures and prevPicOrderCntLsb andprevPicOrderCntMsb are both set equal to 0.

When poc_msb_reset_flag is equal to 1, the PicOrderCntVal of eachpicture that is in the DPB and belongs to the same layer as the currentpicture is decremented by PicOrderCntMsb.

When poc_lsb_reset_flag is equal to 1, the PicOrderCntVal of eachpicture that is in the DPB and belongs to the same layer as the currentpicture is decremented by slice_pic_order_cnt_lsb.

The value of PicOrderCntVal shall be in the range of −231 to 231−1,inclusive. In one CVS, the PicOrderCntVal values for any two codedpictures in the same layer shall not be the same.

The function PicOrderCnt(picX) is specified as follows:

-   -   PicOrderCnt(picX)=PicOrderCntVal of the picture picX

The function DiffPicOrderCnt(picA, picB) is specified as follows:

-   -   DiffPicOrderCnt(picA, pica)=PicOrderCnt(picA)−PicOrderCnt(picB)

The bitstream shall not contain data that result in values ofDiffPicOrderCnt(picA, picB) used in the decoding process that are not inthe range of −215 to 215−1, inclusive.

It should be noted that if X is the current picture and Y and Z are twoother pictures in the same sequence, Y and Z are considered to be in thesame output order direction from X when both DiffPicOrderCnt(X, Y) andDiffPicOrderCnt(X, Z) are positive or both are negative.

Decoding Process for Reference Picture Set

The decoding process for the reference picture set is identical to thedecoding process defined in MV-HEVC WD5.

Example Implementation General SEI Payload Syntax

The following example SEI payload syntax may be used to implement one ormore of the embodiments described herein. In the example below, “XXX”may be replaced with any value representing the payload type that may beutilized in connection with the example syntax. For example, “XXX” maybe replaced with any value between 1 and 255 not already used by anotherSEI message. In another example, the value of “XXX” is not limited to255, and have a higher value. Changes to the existing language in theHEVC specification are shown in italics.

TABLE 2 Example SEI Payload Syntax Descriptor sei_payload( payloadType,payloadSize ) {  if( nal_unit_type = = PREFIX_SEI_NUT )   if(payloadType = = 0 )   ...   else if( payloadType = = XXX )   three_dimensional_reference_displays_info    ( payloadSize )   elseif(payloadType = = XXX)    poc_reset_info( payloadSize )   ...   else   reserved_sei_message( payloadSize )  else /* nal_unit_type = =SUFFIX_SEI_NUT */   if( payloadType = = 3 )    filler_payload(payloadSize )   ...   else    reserved_sei_message( payloadSize )  if(more_data_in_payload( ) ) {   if( payload_extension_present( ) )   reserved_payload_extension_data u(v)   payload_bit_equal_to_one /*equal to 1 */ f(1)   while( !byte_aligned( ) )   payload_bit_equal_to_zero /* equal to 0 */ f(1)  } }

Example Implementation POC Reset Information SEI Message Syntax

The following example POC reset information syntax may be used toimplement one or more of the embodiments described herein. Changes tothe existing language in the HEVC specification are shown in italics.

TABLE 3 Example POC Reset Information Syntax Descriptor poc_reset_info(payloadSize ) {  poc_reset_type_flag u(1)  poc_reset_value u(32) poc_reset_id u(7) }

In some embodiments, poc_reset_value, poc_reset_id, or both, are codedusing exponential-Golomb codes (e.g., ue(v) coding).

Example Implementation POC Reset Information SEI Message Semantics

The following example POC reset information semantics may be used toimplement one or more of the embodiments described herein: “The POCreset information SEI message provides information that enables correctPOC derivation for the associated picture even when the previous picturein decoding order in the same layer as the associated picture and thathas poc_lsb_reset_flag or poc_msb_reset_flag equal to 1 is lost. Theinformation contained in the SEI message can also be used to derive thePOC values of other pictures in the DPB that are in the same layer asthe associated picture. POC-reset picture is defined as a picture thathas the value of either poc_msb_reset_flag or poc_lsb_reset_flag, orboth, equal to 1. The associated POC-reset picture refers to theprevious picture in decoding order in the same layer as the associatedpicture and that has poc_lsb_reset_flag or poc_msb_reset_flag equalto 1. The associated picture of a POC reset information SEI messagerefers to the picture that is associated with the SEI message. Anon-nested POC reset information SEI message is associated with thepicture for which the first VCL NAL unit in decoding order is theassociated VCL NAL unit of the SEI NAL unit containing the non-nestedPOC reset information SEI message. The nuh_layer_id of the SEI NAL unitcontaining a non-nested POC reset information SEI message shall be equalto the nuh_layer_id of the associated picture.”

Alternatively, the association of the SEI message may be defined asfollows: “A non-nested POC reset information SEI message is associatedwith the picture picA in the next access unit in decoding, where picAhas the same value of nuh_layer_id as the SEI NAL unit containing thenon-nested POC reset information SEI message.”

Alternatively, the association of the SEI message may be defined asfollows: “A non-nested POC reset information SEI message is associatedwith the picture picA that has the same value nuh_layer_id as the SEINAL unit, and succeeds, in decoding order, the SEI message and precedesthe first picture that has the same value of nuh_layer_id as the SEI NALunit and has the values of poc_lsb_reset_flag or poc_msb_reset_flag asequal to 1.”

Alternatively, an empty SEI message indicating the cancellation of thePOC reset information (poc_reset_info_cancel( )) may be signaled and theassociation of the SEI message may be defined as follows: “A non-nestedPOC reset information SEI message is associated with the first picturepicA that has the same value of nuh_layer_id as the SEI NAL unit, thatsucceeds the SEI message in decoding order, and that is contained in theaccess unit containing a poc_reset_info_cancel( )) SEI message. Thevalue of nuh_layer_id of the SEI NAL unit containing thepoc_reset_info_cancel( )) SEI message shall be equal to the nuh_layer_idof the associated picture.”

The following semantics may be used for poc_reset_type_flag,poc_reset_value, and poc_reset_id: “poc_reset_type_flag equal to 1indicates that the POC MSB was reset and POC LSB was not reset for theassociated POC-reset picture. poc_reset_type_flag equal to 0 specifiesthat both the POC MSB and POC LSB were reset for the associatedPOC-reset picture; poc_reset_value indicates the POC value of theassociated POC-reset picture before POC resetting is applied (i.e. thederived POC value assuming both poc_msb_reset_flag andpoc_lsb_reset_flag are equal to 0); and poc_reset_id specifies anidentifier of a POC-reset picture in the same layer as the associatedpicture. No two consecutive POC-reset pictures of a particular layer inthe bitstream shall have the same value of poc_reset_id.”

It should be noted that, when the associated POC-reset picture is lost,this value can also be used to derive the POC values of the associatedpicture and other decoded pictures of the same layer in the DPB, asfollows. When the value of poc_reset_type_flag is equal to 0, the POC ofthe associated picture can be derived by setting prevPicOrderCntLsbequal to poc_reset_value % MaxPicOrderCntLsb, and prevPicOrderCntMsbequal to 0, and following the rest of the decoding process for thepicture order count, and the value of PicOrderCntVal of all the picturesin the DPB that belong to the same layer as the associated picture aredecremented by poc_reset_value-poc_reset_value % MaxPicOrderCntLsb. Whenthe value of poc_reset_type_flag is equal to 1, the POC of theassociated picture can be derived by setting prevPicOrderCntLsb andprevPicOrderCntMsb both equal to 0, and following the rest of thedecoding process for the picture order count, and the value ofPicOrderCntVal of all the pictures in the DPB that belong to the samelayer as the associated picture are decremented by poc_reset_value.

In some embodiments, syntax elements similar those described above inconnection with SEI messages are included in the slice segment headersyntax, and the phrase “current picture” is used instead of the phrase“associated picture” in the example semantics described above inconnection with POC reset information SEI message semantics.

Other Considerations

Information and signals disclosed herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the above description may berepresented by voltages, currents, electromagnetic waves, magneticfields or particles, optical fields or particles, or any combinationthereof.

The various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the embodiments disclosedherein may be implemented as electronic hardware, computer software, orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentinvention.

The techniques described herein may be implemented in hardware,software, firmware, or any combination thereof. Such techniques may beimplemented in any of a variety of devices such as general purposescomputers, wireless communication device handsets, or integrated circuitdevices having multiple uses including application in wirelesscommunication device handsets and other devices. Any features describedas modules or components may be implemented together in an integratedlogic device or separately as discrete but interoperable logic devices.If implemented in software, the techniques may be realized at least inpart by a computer-readable data storage medium comprising program codeincluding instructions that, when executed, performs one or more of themethods described above. The computer-readable data storage medium mayform part of a computer program product, which may include packagingmaterials. The computer-readable medium may comprise memory or datastorage media, such as random access memory (RAM) such as synchronousdynamic random access memory (SDRAM), read-only memory (ROM),non-volatile random access memory (NVRAM), electrically erasableprogrammable read-only memory (EEPROM), FLASH memory, magnetic oroptical data storage media, and the like. The techniques additionally,or alternatively, may be realized at least in part by acomputer-readable communication medium that carries or communicatesprogram code in the form of instructions or data structures and that canbe accessed, read, and/or executed by a computer, such as propagatedsignals or waves.

The program code may be executed by a processor, which may include oneor more processors, such as one or more digital signal processors(DSPs), general purpose microprocessors, an application specificintegrated circuits (ASICs), field programmable logic arrays (FPGAs), orother equivalent integrated or discrete logic circuitry. Such aprocessor may be configured to perform any of the techniques describedin this disclosure. A general purpose processor may be a microprocessor;but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration. Accordingly, the term “processor,” as used herein mayrefer to any of the foregoing structure, any combination of theforegoing structure, or any other structure or apparatus suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated software modules or hardware modules configured for encodingand decoding, or incorporated in a combined video encoder-decoder(CODEC). Also, the techniques could be fully implemented in one or morecircuits or logic elements.

The techniques of this disclosure may be implemented in a wide varietyof devices or apparatuses, including a wireless handset, an integratedcircuit (IC) or a set of ICs (e.g., a chip set). Various components,modules, or units are described in this disclosure to emphasizefunctional aspects of devices configured to perform the disclosedtechniques, but do not necessarily require realization by differenthardware units. Rather, as described above, various units may becombined in a codec hardware unit or provided by a collection ofinter-operative hardware units, including one or more processors asdescribed above, in conjunction with suitable software and/or firmware.

Various embodiments of the invention have been described. These andother embodiments are within the scope of the following claims.

What is claimed is:
 1. An apparatus configured to code videoinformation, the apparatus comprising: a memory unit configured to storevideo information associated with a first video layer having a firstpicture; and a processor in communication with the memory unit, theprocessor configured to: process picture order count (POC) derivationinformation associated with the first picture; and determine, based onthe POC derivation information associated with the first picture, a POCvalue of at least one other picture in the first video layer thatprecedes the first picture in decoding order.
 2. The apparatus of claim1, wherein the processor is configured to determine the POC value ofsaid at least one other picture at least in part by: resetting the POCvalue of the at least one other picture using the POC derivationinformation associated with the first picture.
 3. The apparatus of claim1, wherein the memory unit is further configured to store videoinformation associated with a second video layer having a second picturehaving a POC value of zero, wherein the first video layer has a thirdpicture that is in a same access unit as the second picture in thesecond video layer and precedes the first picture in decoding order, andwherein the POC derivation information associated with the first pictureat least comprises a POC value of the third picture.
 4. The apparatus ofclaim 1, wherein the processor is configured to process the POCderivation information at least in part by: processing a POC reset typeflag indicating whether the POC value of the at least one other pictureis to be reset (1) by resetting both one or more most significant bits(MSBs) and one or more least significant bits (LSBs) of the POC value or(2) by resetting only the one or more MSBs of the POC value.
 5. Theapparatus of claim 1, wherein the processor is configured to process thePOC derivation information at least in part by: processing a POC resetvalue indicating a POC value of a second picture in the first videolayer that precedes the first picture in decoding order.
 6. Theapparatus of claim 1, wherein the processor is configured to process thePOC derivation information at least in part by: processing a POC resetID identifying a POC reset with which the POC derivation information isassociated.
 7. The apparatus of claim 1, wherein the processor isconfigured to process the POC derivation information at least in partby: processing an supplemental enhancement information (SEI) messageincluding one or more of a POC reset type flag, a POC reset value, or aPOC reset ID.
 8. The apparatus of claim 1, wherein the processor isconfigured to process the POC derivation information at least in partby: processing a slice header of a slice included in the first picture,the slice header including one or more of a POC reset type flag, a POCreset value, or a POC reset ID.
 9. The apparatus of claim 1, wherein theprocessor is configured to process the POC derivation information atleast in part by: processing one or more of a POC reset type flag, a POCreset value, or a POC reset ID indicated by the POC derivationinformation, at least one of which is coded using exponential-Golombcodes.
 10. The apparatus of claim 1, wherein the apparatus comprises anencoder, and wherein the processor is configured to process the POCderivation information associated with the first picture at least inpart by providing the POC derivation information in association with thefirst picture in a bitstream, and wherein the processor is furtherconfigured to encode the video information in the bitstream.
 11. Theapparatus of claim 1, wherein the apparatus comprises a decoder, whereinthe processor is configured to process the POC derivation informationassociated with the first picture at least in part by the POC derivationinformation in association with the first picture in a bitstream, andwherein the processor is further configured to decode the videoinformation in the bitstream.
 12. The apparatus of claim 1, wherein theapparatus comprises a device selected from a group consisting of one ormore of: a computer, a notebook, a laptop computer, a tablet computer, aset-top box, a telephone handset, a smart phone, a smart pad, atelevision, a camera, a display device, a digital media player, a videogaming console, and an in-car computer.
 13. A method of coding videoinformation, the method comprising: processing picture order count (POC)derivation information associated with a first picture in a first videolayer; and determining, based on the POC derivation informationassociated with the first picture, a POC value of at least one otherpicture in the first video layer that precedes the first picture indecoding order.
 14. The method of claim 13, wherein determining the POCvalue of the at least one other picture at least comprises resetting thePOC value of the at least one other picture using the POC derivationinformation associated with the first picture.
 15. The method of claim13, wherein the POC derivation information associated with the firstpicture at least comprises a POC value of a second picture in the firstvideo layer that precedes the first picture in decoding order, thesecond picture being in a same access unit as a third picture in asecond video layer that has a POC value of zero.
 16. The method of claim13, wherein processing the POC derivation information at least comprisesprocessing a POC reset type flag indicating whether the POC value of theat least one other picture is to be reset (1) by resetting both one ormore most significant bits (MSBs) and one or more least significant bits(LSBs) of the POC value or (2) by resetting only the one or more MSBs ofthe POC value.
 17. The method of claim 13, wherein processing the POCderivation information at least comprises processing a POC reset valueindicating a POC value of a second picture in the first video layer thatprecedes the first picture in decoding order.
 18. The method of claim13, wherein processing the POC derivation information at least comprisesprocessing a POC reset ID identifying a POC reset with which the POCderivation information is associated.
 19. The method of claim 13,wherein processing the POC derivation information at least comprisesprocessing an supplemental enhancement information (SEI) messageincluding one or more of a POC reset type flag, a POC reset value, or aPOC reset ID.
 20. The method of claim 13, wherein processing the POCderivation information at least comprises processing a slice header of aslice included in the first picture, the slice header including one ormore of a POC reset type flag, a POC reset value, or a POC reset ID. 21.The method of claim 13, wherein processing the POC derivationinformation at least comprises processing one or more of a POC resettype flag, a POC reset value, or a POC reset ID indicated by the POCderivation information, at least one of which is coded usingexponential-Golomb codes.
 22. A non-transitory computer readable mediumcomprising code that, when executed, causes an apparatus to perform aprocess comprising: storing video information associated with a firstvideo layer having a first picture; processing picture order count (POC)derivation information associated with the first picture; anddetermining, based on the POC derivation information associated with thefirst picture, a POC value of at least one other picture in the firstvideo layer that precedes the first picture in decoding order.
 23. Thecomputer readable medium of claim 22, wherein determining the POC valueof the at least one other picture at least comprises resetting the POCvalue of the at least one other picture using the POC derivationinformation associated with the first picture.
 24. The computer readablemedium of claim 22, wherein the process further comprises: storing videoinformation associated with a second video layer having a second picturehaving a POC value of zero, wherein the first video layer has a thirdpicture that is in a same access unit as the second picture in thesecond video layer and precedes the first picture in decoding order, andwherein the POC derivation information associated with the first pictureat least comprises a POC value of the third picture.
 25. The computerreadable medium of claim 22, wherein processing the POC derivationinformation at least comprises processing a slice header of a sliceincluded in the first picture, the slice header including one or more ofa POC reset type flag, a POC reset value, or a POC reset.
 26. A videocoding device configured to code video information, the video codingdevice comprising: means for storing video information associated with afirst video layer having a first picture; means for processing pictureorder count (POC) derivation information associated with the firstpicture; and means for determining, based on the POC derivationinformation associated with the first picture, a POC value of at leastone other picture in the first video layer that precedes the firstpicture in decoding order.
 27. The video coding device of claim 26,wherein the means for determining the POC value of the at least oneother picture at least comprises means for resetting the POC value ofthe at least one other picture using the POC derivation informationassociated with the first picture.
 28. The video coding device of claim26, further comprising means for storing video information associatedwith a second video layer having a second picture having a POC value ofzero, wherein the first video layer has a third picture that is in asame access unit as the second picture in the second video layer andprecedes the first picture in decoding order, and wherein the POCderivation information associated with the first picture at leastcomprises a POC value of the third picture.
 29. The video coding deviceof claim 26, wherein the means for determining the POC value of the atleast one other picture at least comprises means for processing a sliceheader of a slice included in the first picture, the slice headerincluding one or more of a POC reset type flag, a POC reset value, or aPOC reset.